/**************************************************************************** * fs/fat/fs_fat32util.c * * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. The * ASF licenses this file to you under the Apache License, Version 2.0 (the * "License"); you may not use this file except in compliance with the * License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the * License for the specific language governing permissions and limitations * under the License. * ****************************************************************************/ /**************************************************************************** * Included Files ****************************************************************************/ #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include "inode/inode.h" #include "fs_fat32.h" /**************************************************************************** * Private Functions ****************************************************************************/ /**************************************************************************** * Name: fat_checkfsinfo * * Description: * Read the FAT32 FSINFO sector * ****************************************************************************/ static int fat_checkfsinfo(struct fat_mountpt_s *fs) { /* Make sure that the fsinfo sector is in the cache */ if (fat_fscacheread(fs, fs->fs_fsinfo) == OK) { /* Verify that this is, indeed, an FSINFO sector */ if (FSI_GETLEADSIG(fs->fs_buffer) == 0x41615252 && FSI_GETSTRUCTSIG(fs->fs_buffer) == 0x61417272 && FSI_GETTRAILSIG(fs->fs_buffer) == BOOT_SIGNATURE32) { fs->fs_fsifreecount = FSI_GETFREECOUNT(fs->fs_buffer); fs->fs_fsinextfree = FSI_GETNXTFREE(fs->fs_buffer); return OK; } } return -ENODEV; } /**************************************************************************** * Name: fat_checkbootrecord * * Description: * Verify that that currently buffer sector is a valid FAT boot record. * This may refer to either the older (pre-partition) MBR sector that lies * at sector one or to the more common FBR that lies at the beginning of * the partition. * * NOTE: The more common FBR naming is used in the file even when parsing * an MBR. This is possible because the field offsets and meaning are * identical. * ****************************************************************************/ static int fat_checkbootrecord(struct fat_mountpt_s *fs) { uint32_t ndatasectors; uint32_t ntotalfatsects; uint16_t rootdirsectors = 0; bool notfat32 = false; /* Verify the MBR signature at offset 510 in the sector (true even * if the sector size is greater than 512. All FAT file systems have * this signature. On a FAT32 volume, the RootEntCount , FatSz16, and * FatSz32 values should always be zero. The FAT sector size should * match the reported hardware sector size. */ if (FBR_GETSIGNATURE(fs->fs_buffer) != BOOT_SIGNATURE16 || FBR_GETBYTESPERSEC(fs->fs_buffer) != fs->fs_hwsectorsize) { fwarn("WARNING: Signature: %04x FS sectorsize: %d " "HW sectorsize: %" PRIdOFF "\n", FBR_GETSIGNATURE(fs->fs_buffer), FBR_GETBYTESPERSEC(fs->fs_buffer), fs->fs_hwsectorsize); return -EINVAL; } /* Verify the FAT32 file system type. The determination of the file * system type is based on the number of clusters on the volume: FAT12 * volume has <= FAT_MAXCLUST12 (4084) clusters, a FAT16 volume has <= * FAT_MAXCLUST16 (Microsoft says < 65,525) clusters, and any larger * is FAT32. * * Get the number of 32-bit directory entries in root directory (zero * for FAT32). */ fs->fs_rootentcnt = FBR_GETROOTENTCNT(fs->fs_buffer); if (fs->fs_rootentcnt != 0) { notfat32 = true; /* Must be zero for FAT32 */ rootdirsectors = (32 * fs->fs_rootentcnt + fs->fs_hwsectorsize - 1) / fs->fs_hwsectorsize; } /* Determine the number of sectors in a FAT. */ fs->fs_nfatsects = FBR_GETFATSZ16(fs->fs_buffer); /* Should be zero */ if (fs->fs_nfatsects) { notfat32 = true; /* Must be zero for FAT32 */ } else { fs->fs_nfatsects = FBR_GETFATSZ32(fs->fs_buffer); } if (!fs->fs_nfatsects || fs->fs_nfatsects >= fs->fs_hwnsectors) { fwarn("WARNING: fs_nfatsects %" PRId32 " fs_hwnsectors: %" PRIdOFF "\n", fs->fs_nfatsects, fs->fs_hwnsectors); return -EINVAL; } /* Get the total number of sectors on the volume. */ fs->fs_fattotsec = FBR_GETTOTSEC16(fs->fs_buffer); /* Should be zero */ if (fs->fs_fattotsec) { notfat32 = true; /* Must be zero for FAT32 */ } else { fs->fs_fattotsec = FBR_GETTOTSEC32(fs->fs_buffer); } if (!fs->fs_fattotsec || fs->fs_fattotsec > fs->fs_hwnsectors) { fwarn("WARNING: fs_fattotsec %" PRId32 " fs_hwnsectors: %" PRIdOFF "\n", fs->fs_fattotsec, fs->fs_hwnsectors); return -EINVAL; } /* Get the total number of reserved sectors */ fs->fs_fatresvdseccount = FBR_GETRESVDSECCOUNT(fs->fs_buffer); if (fs->fs_fatresvdseccount > fs->fs_hwnsectors) { fwarn("WARNING: fs_fatresvdseccount %d" " fs_hwnsectors: %" PRIdOFF "\n", fs->fs_fatresvdseccount, fs->fs_hwnsectors); return -EINVAL; } /* Get the number of FATs. This is probably two but could have other * values. */ fs->fs_fatnumfats = FBR_GETNUMFATS(fs->fs_buffer); ntotalfatsects = fs->fs_fatnumfats * fs->fs_nfatsects; /* Get the total number of data sectors */ ndatasectors = fs->fs_fattotsec - fs->fs_fatresvdseccount - ntotalfatsects - rootdirsectors; if (ndatasectors > fs->fs_hwnsectors) { fwarn("WARNING: ndatasectors %" PRId32 " fs_hwnsectors: %" PRIdOFF "\n", ndatasectors, fs->fs_hwnsectors); return -EINVAL; } /* Get the sectors per cluster */ fs->fs_fatsecperclus = FBR_GETSECPERCLUS(fs->fs_buffer); /* Calculate the number of clusters */ fs->fs_nclusters = ndatasectors / fs->fs_fatsecperclus; /* Finally, the test: */ if (fs->fs_nclusters <= FAT_MAXCLUST12) { fs->fs_fsinfo = 0; fs->fs_type = FSTYPE_FAT12; } else if (fs->fs_nclusters <= FAT_MAXCLUST16) { fs->fs_fsinfo = 0; fs->fs_type = FSTYPE_FAT16; } else if (!notfat32) { fs->fs_fsinfo = fs->fs_fatbase + FBR_GETFSINFO(fs->fs_buffer); fs->fs_type = FSTYPE_FAT32; } else { fwarn("WARNING: notfat32: %d fs_nclusters: %" PRId32 "\n", notfat32, fs->fs_nclusters); return -EINVAL; } /* We have what appears to be a valid FAT filesystem! Save a few more * things from the boot record that we will need later. */ fs->fs_fatbase += fs->fs_fatresvdseccount; if (fs->fs_type == FSTYPE_FAT32) { fs->fs_rootbase = FBR_GETROOTCLUS(fs->fs_buffer); } else { fs->fs_rootbase = fs->fs_fatbase + ntotalfatsects; } fs->fs_database = fs->fs_fatbase + ntotalfatsects + fs->fs_rootentcnt / DIRSEC_NDIRS(fs); fs->fs_fsifreecount = 0xffffffff; return OK; } /**************************************************************************** * Public Functions ****************************************************************************/ /**************************************************************************** * Name: fat_getuint16 ****************************************************************************/ uint16_t fat_getuint16(uint8_t *ptr) { /* NOTE that (1) this operation is independent of endian-ness and that (2) * byte-by-byte transfer is necessary in any case because the address may * be unaligned. */ return ((uint16_t)ptr[1] << 8) | ptr[0]; } /**************************************************************************** * Name: fat_getuint32 ****************************************************************************/ uint32_t fat_getuint32(uint8_t *ptr) { /* NOTE that (1) this operation is independent of endian-ness and that (2) * byte-by-byte transfer is necessary in any case because the address may * be unaligned. */ return ((uint32_t)fat_getuint16(&ptr[2]) << 16) | fat_getuint16(&ptr[0]); } /**************************************************************************** * Name: fat_putuint16 ****************************************************************************/ void fat_putuint16(FAR uint8_t *ptr, uint16_t value16) { FAR uint8_t *val = (FAR uint8_t *)&value16; #ifdef CONFIG_ENDIAN_BIG /* If the target is big-endian then the bytes always have to be swapped so * that the representation is little endian in the file system. */ ptr[0] = val[1]; ptr[1] = val[0]; #else /* Byte-by-byte transfer is still necessary because the address may be * un-aligned. */ ptr[0] = val[0]; ptr[1] = val[1]; #endif } /**************************************************************************** * Name: fat_putuint32 ****************************************************************************/ void fat_putuint32(FAR uint8_t *ptr, uint32_t value32) { FAR uint16_t *val = (FAR uint16_t *)&value32; #ifdef CONFIG_ENDIAN_BIG /* If the target is big-endian then the bytes always have to be swapped so * that the representation is little endian in the file system. */ fat_putuint16(&ptr[0], val[1]); fat_putuint16(&ptr[2], val[0]); #else /* Byte-by-byte transfer is still necessary because the address may be * un-aligned. */ fat_putuint16(&ptr[0], val[0]); fat_putuint16(&ptr[2], val[1]); #endif } /**************************************************************************** * Name: fat_semtake ****************************************************************************/ int fat_semtake(struct fat_mountpt_s *fs) { return nxsem_wait_uninterruptible(&fs->fs_sem); } /**************************************************************************** * Name: fat_semgive ****************************************************************************/ void fat_semgive(struct fat_mountpt_s *fs) { nxsem_post(&fs->fs_sem); } /**************************************************************************** * Name: fat_systime2fattime * * Description: * Get the system time convert to a time and and date suitable for * writing into the FAT FS. * * TIME in LS 16-bits: * Bits 0:4 = 2 second count (0-29 representing 0-58 seconds) * Bits 5-10 = minutes (0-59) * Bits 11-15 = hours (0-23) * DATE in MS 16-bits * Bits 0:4 = Day of month (1-31) * Bits 5:8 = Month of year (1-12) * Bits 9:15 = Year from 1980 (0-127 representing 1980-2107) * ****************************************************************************/ uint32_t fat_systime2fattime(void) { /* Unless you have a hardware RTC or some other to get accurate time, then * there is no reason to support FAT time. */ #ifdef CONFIG_FS_FATTIME struct timespec ts; struct tm tm; int ret; /* Get the current time in seconds and nanoseconds */ ret = clock_gettime(CLOCK_REALTIME, &ts); if (ret == OK) { /* Break done the seconds in date and time units */ if (gmtime_r((FAR const time_t *)&ts.tv_sec, &tm) != NULL) { /* FAT can only represent dates since 1980. struct tm can * represent dates since 1900. */ if (tm.tm_year >= 80) { uint16_t fattime; uint16_t fatdate; fattime = (tm.tm_sec >> 1) & 0x001f; /* Bits 0-4: 2 second count (0-29) */ fattime |= (tm.tm_min << 5) & 0x07e0; /* Bits 5-10: minutes (0-59) */ fattime |= (tm.tm_hour << 11) & 0xf800; /* Bits 11-15: hours (0-23) */ fatdate = tm.tm_mday & 0x001f; /* Bits 0-4: Day of month (1-31) */ fatdate |= ((tm.tm_mon + 1) << 5) & 0x01e0; /* Bits 5-8: Month of year (1-12) */ fatdate |= ((tm.tm_year - 80) << 9) & 0xfe00; /* Bits 9-15: Year from 1980 */ return (uint32_t)fatdate << 16 | (uint32_t)fattime; } } } #endif return 0; } /**************************************************************************** * Name: fat_fattime2systime * * Description: * Convert FAT data and time to a system time_t * * 16-bit FAT time: * Bits 0:4 = 2 second count (0-29 representing 0-58 seconds) * Bits 5-10 = minutes (0-59) * Bits 11-15 = hours (0-23) * 16-bit FAT date: * Bits 0:4 = Day of month (1-31) * Bits 5:8 = Month of year (1-12) * Bits 9:15 = Year from 1980 (0-127 representing 1980-2107) * ****************************************************************************/ time_t fat_fattime2systime(uint16_t fattime, uint16_t fatdate) { /* Unless you have a hardware RTC or some other to get accurate time, then * there is no reason to support FAT time. */ #ifdef CONFIG_FS_FATTIME struct tm tm; unsigned int tmp; /* Break out the date and time */ tm.tm_sec = (fattime & 0x001f) << 1; /* Bits 0-4: 2 second count (0-29) */ tm.tm_min = (fattime & 0x07e0) >> 5; /* Bits 5-10: minutes (0-59) */ tm.tm_hour = (fattime & 0xf800) >> 11; /* Bits 11-15: hours (0-23) */ tm.tm_mday = (fatdate & 0x001f); /* Bits 0-4: Day of month (1-31) */ tmp = ((fatdate & 0x01e0) >> 5); /* Bits 5-8: Month of year (1-12) */ tm.tm_mon = tmp > 0 ? tmp - 1 : 0; tm.tm_year = ((fatdate & 0xfe00) >> 9) + 80; /* Bits 9-15: Year from 1980 */ /* Then convert the broken out time into seconds since the epoch */ return timegm(&tm); #else return 0; #endif } /**************************************************************************** * Name: fat_mount * * Description: * This function is called only when the mountpoint is first established. * It initializes the mountpoint structure and verifies that a valid FAT32 * filesystem is provided by the block driver. * * The caller should hold the mountpoint semaphore * ****************************************************************************/ int fat_mount(struct fat_mountpt_s *fs, bool writeable) { FAR struct inode *inode; struct geometry geo; int ret; /* Assume that the mount is successful */ fs->fs_mounted = true; /* Check if there is media available */ inode = fs->fs_blkdriver; if (!inode || !inode->u.i_bops || !inode->u.i_bops->geometry || inode->u.i_bops->geometry(inode, &geo) != OK || !geo.geo_available) { ret = -ENODEV; goto errout; } /* Make sure that that the media is write-able (if write access is * needed). */ if (writeable && !geo.geo_writeenabled) { ret = -EACCES; goto errout; } /* Save the hardware geometry */ fs->fs_hwsectorsize = geo.geo_sectorsize; fs->fs_hwnsectors = geo.geo_nsectors; /* Allocate a buffer to hold one hardware sector */ fs->fs_buffer = (FAR uint8_t *)fat_io_alloc(fs->fs_hwsectorsize); if (!fs->fs_buffer) { ret = -ENOMEM; goto errout; } /* Search FAT boot record on the drive. First check the MBR at sector * zero. This could be either the boot record or a partition that refers * to the boot record. * * First read sector zero. This will be the first access to the drive and * a likely failure point. */ fs->fs_fatbase = 0; ret = fat_hwread(fs, fs->fs_buffer, 0, 1); if (ret < 0) { goto errout_with_buffer; } /* Older style MBR (pre-partition table) includes boot information for the * partition-less drive. Check for that case first. */ ret = fat_checkbootrecord(fs); if (ret != OK) { /* The contents of sector 0 is not a boot record. It could be have * DOS partitions, however. Get the offset into the partition table. * This table is at offset MBR_TABLE and is indexed by 16x the * partition number. */ int i; for (i = 0; i < 4; i++) { /* Check if the partition exists and, if so, get the bootsector for * that partition and see if we can find the boot record there. */ uint8_t part = PART_GETTYPE(i, fs->fs_buffer); finfo("Partition %d, offset %d, type %d\n", i, PART_ENTRY(i), part); if (part == 0) { finfo("No partition %d\n", i); continue; } /* There appears to be a partition, get the sector number of the * partition (LBA) */ fs->fs_fatbase = PART_GETSTARTSECTOR(i, fs->fs_buffer); /* Read the new candidate boot sector */ ret = fat_hwread(fs, fs->fs_buffer, fs->fs_fatbase, 1); if (ret < 0) { /* Failed to read the sector */ ferr("ERROR: Failed to read sector %ld: %d\n", (long)fs->fs_fatbase, ret); continue; } /* Check if this is a boot record */ ret = fat_checkbootrecord(fs); if (ret == OK) { /* Break out of the loop if a valid boot record is found */ finfo("FBR found in partition %d\n", i); break; } /* Re-read sector 0 so that we can check the next partition */ finfo("Partition %d is not an FBR\n", i); ret = fat_hwread(fs, fs->fs_buffer, 0, 1); if (ret < 0) { ferr("ERROR: Failed to re-read sector 0: %d\n", ret); goto errout_with_buffer; } } if (i > 3) { ferr("ERROR: No valid boot record\n"); ret = -EINVAL; goto errout_with_buffer; } } /* We have what appears to be a valid FAT filesystem! Now read the * FSINFO sector (FAT32 only) */ if (fs->fs_type == FSTYPE_FAT32) { ret = fat_checkfsinfo(fs); if (ret != OK) { goto errout_with_buffer; } } /* Enforce computation of free clusters if configured */ #ifdef CONFIG_FAT_COMPUTE_FSINFO ret = fat_computefreeclusters(fs); if (ret != OK) { goto errout_with_buffer; } #endif /* We did it! */ finfo("FAT%d:\n", fs->fs_type == 0 ? 12 : fs->fs_type == 1 ? 16 : 32); finfo("\tHW sector size: %" PRIdOFF "\n", fs->fs_hwsectorsize); finfo("\t sectors: %" PRIdOFF "\n", fs->fs_hwnsectors); finfo("\tFAT reserved: %d\n", fs->fs_fatresvdseccount); finfo("\t sectors: %" PRId32 "\n", fs->fs_fattotsec); finfo("\t start sector: %" PRIdOFF "\n", fs->fs_fatbase); finfo("\t root sector: %" PRIdOFF "\n", fs->fs_rootbase); finfo("\t root entries: %d\n", fs->fs_rootentcnt); finfo("\t data sector: %" PRIdOFF "\n", fs->fs_database); finfo("\t FSINFO sector: %" PRIdOFF "\n", fs->fs_fsinfo); finfo("\t Num FATs: %d\n", fs->fs_fatnumfats); finfo("\t FAT sectors: %" PRId32 "\n", fs->fs_nfatsects); finfo("\t sectors/cluster: %d\n", fs->fs_fatsecperclus); finfo("\t max clusters: %" PRId32 "\n", fs->fs_nclusters); finfo("\tFSI free count %" PRId32 "\n", fs->fs_fsifreecount); finfo("\t next free %" PRId32 "\n", fs->fs_fsinextfree); return OK; errout_with_buffer: fat_io_free(fs->fs_buffer, fs->fs_hwsectorsize); fs->fs_buffer = 0; errout: fs->fs_mounted = false; return ret; } /**************************************************************************** * Name: fat_checkmount * * Description: * Check if the mountpoint is still valid. * * The caller should hold the mountpoint semaphore * ****************************************************************************/ int fat_checkmount(struct fat_mountpt_s *fs) { /* If the fs_mounted flag is false, then we have already handled the loss * of the mount. */ if (fs && fs->fs_mounted) { /* We still think the mount is healthy. Check an see if this is * still the case */ if (fs->fs_blkdriver) { struct inode *inode = fs->fs_blkdriver; if (inode && inode->u.i_bops && inode->u.i_bops->geometry) { struct geometry geo; int errcode = inode->u.i_bops->geometry(inode, &geo); if (errcode == OK && geo.geo_available && !geo.geo_mediachanged) { return OK; } } } /* If we get here, the mount is NOT healthy */ fs->fs_mounted = false; } return -ENODEV; } /**************************************************************************** * Name: fat_hwread * * Description: * Read the specified sector into the sector buffer * ****************************************************************************/ int fat_hwread(struct fat_mountpt_s *fs, uint8_t *buffer, off_t sector, unsigned int nsectors) { int ret = -ENODEV; if (fs && fs->fs_blkdriver) { struct inode *inode = fs->fs_blkdriver; if (inode && inode->u.i_bops && inode->u.i_bops->read) { ssize_t nsectorsread = inode->u.i_bops->read(inode, buffer, sector, nsectors); if (nsectorsread == nsectors) { ret = OK; } else if (nsectorsread < 0) { ret = nsectorsread; } } } return ret; } /**************************************************************************** * Name: fat_hwwrite * * Description: * Write the sector buffer to the specified sector * ****************************************************************************/ int fat_hwwrite(struct fat_mountpt_s *fs, uint8_t *buffer, off_t sector, unsigned int nsectors) { int ret = -ENODEV; if (fs && fs->fs_blkdriver) { struct inode *inode = fs->fs_blkdriver; if (inode && inode->u.i_bops && inode->u.i_bops->write) { ssize_t nsectorswritten = inode->u.i_bops->write(inode, buffer, sector, nsectors); if (nsectorswritten == nsectors) { ret = OK; } else if (nsectorswritten < 0) { ret = nsectorswritten; } } } return ret; } /**************************************************************************** * Name: fat_cluster2sector * * Description: * Convert a cluster number to a start sector number * ****************************************************************************/ off_t fat_cluster2sector(FAR struct fat_mountpt_s *fs, uint32_t cluster) { cluster -= 2; if (cluster >= fs->fs_nclusters - 2) { return -EINVAL; } return cluster * fs->fs_fatsecperclus + fs->fs_database; } /**************************************************************************** * Name: fat_getcluster * * Description: * Get the next cluster start from the FAT. * * Returned Value: * <0: error, 0:cluster unassigned, >=0: start sector of cluster * ****************************************************************************/ off_t fat_getcluster(struct fat_mountpt_s *fs, uint32_t clusterno) { /* Verify that the cluster number is within range */ if (clusterno >= 2 && clusterno < fs->fs_nclusters) { /* Okay.. Read the next cluster from the FAT. The way we will do * this depends on the type of FAT filesystem we are dealing with. */ switch (fs->fs_type) { case FSTYPE_FAT12 : { off_t fatsector; unsigned int fatoffset; unsigned int cluster; unsigned int fatindex; /* FAT12 is more complex because it has 12-bits (1.5 bytes) * per FAT entry. Get the offset to the first byte: */ fatoffset = (clusterno * 3) / 2; fatsector = fs->fs_fatbase + SEC_NSECTORS(fs, fatoffset); /* Read the sector at this offset */ if (fat_fscacheread(fs, fatsector) < 0) { /* Read error */ break; } /* Get the first, LS byte of the cluster from the FAT */ fatindex = fatoffset & SEC_NDXMASK(fs); cluster = fs->fs_buffer[fatindex]; /* With FAT12, the second byte of the cluster number may lie in * a different sector than the first byte. */ fatindex++; if (fatindex >= fs->fs_hwsectorsize) { fatsector++; fatindex = 0; if (fat_fscacheread(fs, fatsector) < 0) { /* Read error */ break; } } /* Get the second, MS byte of the cluster for 16-bits. The * does not depend on the endian-ness of the target, but only * on the fact that the byte stream is little-endian. */ cluster |= (unsigned int)fs->fs_buffer[fatindex] << 8; /* Now, pick out the correct 12 bit cluster start sector * value. */ if ((clusterno & 1) != 0) { /* Odd.. take the MS 12-bits */ cluster >>= 4; } else { /* Even.. take the LS 12-bits */ cluster &= 0x0fff; } return cluster; } case FSTYPE_FAT16 : { unsigned int fatoffset = 2 * clusterno; off_t fatsector = fs->fs_fatbase + SEC_NSECTORS(fs, fatoffset); unsigned int fatindex = fatoffset & SEC_NDXMASK(fs); if (fat_fscacheread(fs, fatsector) < 0) { /* Read error */ break; } return FAT_GETFAT16(fs->fs_buffer, fatindex); } case FSTYPE_FAT32 : { unsigned int fatoffset = 4 * clusterno; off_t fatsector = fs->fs_fatbase + SEC_NSECTORS(fs, fatoffset); unsigned int fatindex = fatoffset & SEC_NDXMASK(fs); if (fat_fscacheread(fs, fatsector) < 0) { /* Read error */ break; } return FAT_GETFAT32(fs->fs_buffer, fatindex) & 0x0fffffff; } default: break; } } /* There is no cluster information, or an error occurred */ return (off_t)-EINVAL; } /**************************************************************************** * Name: fat_putcluster * * Description: * Write a new cluster into the FAT * ****************************************************************************/ int fat_putcluster(struct fat_mountpt_s *fs, uint32_t clusterno, off_t nextcluster) { /* Verify that the cluster number is within range. Zero erases the * cluster. */ if (clusterno == 0 || (clusterno >= 2 && clusterno < fs->fs_nclusters)) { /* Okay.. Write the next cluster into the FAT. The way we will do * this depends on the type of FAT filesystem we are dealing with. */ switch (fs->fs_type) { case FSTYPE_FAT12 : { off_t fatsector; unsigned int fatoffset; unsigned int fatindex; uint8_t value; /* FAT12 is more complex because it has 12-bits (1.5 bytes) * per FAT entry. Get the offset to the first byte: */ fatoffset = (clusterno * 3) / 2; fatsector = fs->fs_fatbase + SEC_NSECTORS(fs, fatoffset); /* Make sure that the sector at this offset is in the cache */ if (fat_fscacheread(fs, fatsector) < 0) { /* Read error */ break; } /* Get the LS byte first handling the 12-bit alignment within * the 16-bits */ fatindex = fatoffset & SEC_NDXMASK(fs); if ((clusterno & 1) != 0) { /* Save the LS four bits of the next cluster */ value = (fs->fs_buffer[fatindex] & 0x0f) | nextcluster << 4; } else { /* Save the LS eight bits of the next cluster */ value = (uint8_t)nextcluster; } fs->fs_buffer[fatindex] = value; /* With FAT12, the second byte of the cluster number may lie in * a different sector than the first byte. */ fatindex++; if (fatindex >= fs->fs_hwsectorsize) { /* Read the next sector */ fatsector++; fatindex = 0; /* Set the dirty flag to make sure the sector that we * just modified is written out. */ fs->fs_dirty = true; if (fat_fscacheread(fs, fatsector) < 0) { /* Read error */ break; } } /* Output the MS byte first handling the 12-bit alignment * within the 16-bits */ if ((clusterno & 1) != 0) { /* Save the MS eight bits of the next cluster */ value = (uint8_t)(nextcluster >> 4); } else { /* Save the MS four bits of the next cluster */ value = (fs->fs_buffer[fatindex] & 0xf0) | ((nextcluster >> 8) & 0x0f); } fs->fs_buffer[fatindex] = value; } break; case FSTYPE_FAT16 : { unsigned int fatoffset = 2 * clusterno; off_t fatsector = fs->fs_fatbase + SEC_NSECTORS(fs, fatoffset); unsigned int fatindex = fatoffset & SEC_NDXMASK(fs); if (fat_fscacheread(fs, fatsector) < 0) { /* Read error */ break; } FAT_PUTFAT16(fs->fs_buffer, fatindex, nextcluster & 0xffff); } break; case FSTYPE_FAT32 : { unsigned int fatoffset = 4 * clusterno; off_t fatsector = fs->fs_fatbase + SEC_NSECTORS(fs, fatoffset); unsigned int fatindex = fatoffset & SEC_NDXMASK(fs); uint32_t val; if (fat_fscacheread(fs, fatsector) < 0) { /* Read error */ break; } /* Keep the top 4 bits */ val = FAT_GETFAT32(fs->fs_buffer, fatindex) & 0xf0000000; FAT_PUTFAT32(fs->fs_buffer, fatindex, val | (nextcluster & 0x0fffffff)); } break; default: return -EINVAL; } /* Mark the modified sector as "dirty" and return success */ fs->fs_dirty = true; return OK; } return -EINVAL; } /**************************************************************************** * Name: fat_removechain * * Description: * Remove an entire chain of clusters, starting with 'cluster' * ****************************************************************************/ int fat_removechain(struct fat_mountpt_s *fs, uint32_t cluster) { int32_t nextcluster; int ret; /* Loop while there are clusters in the chain */ while (cluster >= 2 && cluster < fs->fs_nclusters) { /* Get the next cluster after the current one */ nextcluster = fat_getcluster(fs, cluster); if (nextcluster < 0) { /* Error! */ return nextcluster; } /* Then nullify current cluster -- removing it from the chain */ ret = fat_putcluster(fs, cluster, 0); if (ret < 0) { return ret; } /* Update FSINFINFO data */ if (fs->fs_fsifreecount != 0xffffffff) { fs->fs_fsifreecount++; fs->fs_fsidirty = true; } /* Then set up to remove the next cluster */ cluster = nextcluster; } return OK; } /**************************************************************************** * Name: fat_extendchain * * Description: * Add a new cluster to the chain following cluster (if cluster is non- * NULL). if cluster is zero, then a new chain is created. * * Returned Value: * <0:error, 0: no free cluster, >=2: new cluster number * ****************************************************************************/ int32_t fat_extendchain(struct fat_mountpt_s *fs, uint32_t cluster) { off_t startsector; uint32_t newcluster; uint32_t startcluster; int ret; /* The special value 0 is used when the new chain should start */ if (cluster == 0) { /* The FSINFO NextFree entry should be a good starting point * in the search for a new cluster */ startcluster = fs->fs_fsinextfree; if (startcluster == 0 || startcluster >= fs->fs_nclusters) { /* But it is bad.. we have to start at the beginning */ startcluster = 1; } } else { /* We are extending an existing chain. Verify that this * is a valid cluster by examining its start sector. */ startsector = fat_getcluster(fs, cluster); if (startsector < 0) { /* An error occurred, return the error value */ return startsector; } else if (startsector < 2) { /* Oops.. this cluster does not exist. */ return 0; } else if (startsector < fs->fs_nclusters) { /* It is already followed by next cluster */ return startsector; } /* Okay.. it checks out */ startcluster = cluster; } /* Loop until (1) we discover that there are not free clusters * (return 0), an errors occurs (return -errno), or (3) we find * the next cluster (return the new cluster number). */ newcluster = startcluster; for (; ; ) { /* Examine the next cluster in the FAT */ newcluster++; if (newcluster >= fs->fs_nclusters) { /* If we hit the end of the available clusters, then * wrap back to the beginning because we might have * started at a non-optimal place. But don't continue * past the start cluster. */ newcluster = 2; if (newcluster > startcluster) { /* We are back past the starting cluster, then there * is no free cluster. */ return 0; } } /* We have a candidate cluster. Check if the cluster number is * mapped to a group of sectors. */ startsector = fat_getcluster(fs, newcluster); if (startsector == 0) { /* Found have found a free cluster break out */ break; } else if (startsector < 0) { /* Some error occurred, return the error number */ return startsector; } /* We wrap all the back to the starting cluster? If so, then * there are no free clusters. */ if (newcluster == startcluster) { return 0; } } /* We get here only if we break out with an available cluster * number in 'newcluster' Now mark that cluster as in-use. */ ret = fat_putcluster(fs, newcluster, 0x0fffffff); if (ret < 0) { /* An error occurred */ return ret; } /* And link if to the start cluster (if any) */ if (cluster) { /* There is a start cluster -- link it */ ret = fat_putcluster(fs, cluster, newcluster); if (ret < 0) { return ret; } } /* And update the FINSINFO for the next time we have to search */ fs->fs_fsinextfree = newcluster; if (fs->fs_fsifreecount != 0xffffffff) { fs->fs_fsifreecount--; fs->fs_fsidirty = true; } /* Return then number of the new cluster that was added to the chain */ return newcluster; } /**************************************************************************** * Name: fat_nextdirentry * * Description: * Read the next directory entry from the sector in cache, reading the * next sector(s) in the cluster as necessary. This function must * return -ENOSPC if it fails because there are no further entries * available in the directory. * ****************************************************************************/ int fat_nextdirentry(struct fat_mountpt_s *fs, struct fs_fatdir_s *dir) { unsigned int cluster; unsigned int ndx; /* Increment the index to the next 32-byte directory entry */ ndx = dir->fd_index + 1; /* Check if all of the directory entries in this sectory have * been examined. */ if ((ndx & (DIRSEC_NDIRS(fs)-1)) == 0) { /* Yes, then we will have to read the next sector */ dir->fd_currsector++; /* For FAT12/16, the root directory is a group of sectors relative * to the first sector of the fat volume. */ if (!dir->fd_currcluster) { /* For FAT12/16, the boot record tells us number of 32-bit * directories that are contained in the root directory. This * should correspond to an even number of sectors. */ if (ndx >= fs->fs_rootentcnt) { /* When we index past this count, we have examined all of the * entries in the root directory. */ return -ENOSPC; } } else { /* Not a FAT12/16 root directory, check if we have examined the * entire cluster comprising the directory. * * The current sector within the cluster is the entry number * divided byte the number of entries per sector */ int sector = ndx / DIRSEC_NDIRS(fs); /* We are finished with the cluster when the last sector of the * cluster has been examined. */ if ((sector & (fs->fs_fatsecperclus - 1)) == 0) { /* Get next cluster */ cluster = fat_getcluster(fs, dir->fd_currcluster); /* Check if a valid cluster was obtained. */ if (cluster < 2 || cluster >= fs->fs_nclusters) { /* No, we have probably reached the end of the cluster * list. */ return -ENOSPC; } /* Initialize for new cluster */ dir->fd_currcluster = cluster; dir->fd_currsector = fat_cluster2sector(fs, cluster); ndx = 0; } } } /* Save the new index into dir->fd_currsector */ dir->fd_index = ndx; return OK; } /**************************************************************************** * Name: fat_dirtruncate * * Description: * Truncate an existing file to zero length. * * Assumptions: * The caller holds mountpoint semaphore, fs_buffer holds the directory * entry, the directory entry sector (fd_sector) is currently in the * sector cache. * ****************************************************************************/ int fat_dirtruncate(struct fat_mountpt_s *fs, FAR uint8_t *direntry) { unsigned int startcluster; uint32_t writetime; off_t savesector; int ret; /* Get start cluster of the file to truncate */ startcluster = ((uint32_t)DIR_GETFSTCLUSTHI(direntry) << 16) | DIR_GETFSTCLUSTLO(direntry); /* Clear the cluster start value in the directory and set the file size * to zero. This makes the file look empty but also have to dispose of * all of the clusters in the chain. */ DIR_PUTFSTCLUSTHI(direntry, 0); DIR_PUTFSTCLUSTLO(direntry, 0); DIR_PUTFILESIZE(direntry, 0); /* Set the ARCHIVE attribute and update the write time */ DIR_PUTATTRIBUTES(direntry, FATATTR_ARCHIVE); writetime = fat_systime2fattime(); DIR_PUTWRTTIME(direntry, writetime & 0xffff); DIR_PUTWRTDATE(direntry, writetime >> 16); /* This sector needs to be written back to disk eventually */ fs->fs_dirty = true; /* Now remove the entire cluster chain comprising the file */ savesector = fs->fs_currentsector; ret = fat_removechain(fs, startcluster); if (ret < 0) { return ret; } /* Setup FSINFO to reuse the old start cluster next */ fs->fs_fsinextfree = startcluster - 1; /* Make sure that the directory is still in the cache */ return fat_fscacheread(fs, savesector); } /**************************************************************************** * Name: fat_dirshrink * * Description: * Shrink the size existing file to a non-zero length * * Assumptions: * The caller holds mountpoint semaphore, fs_buffer holds the directory * entry. * ****************************************************************************/ int fat_dirshrink(struct fat_mountpt_s *fs, FAR uint8_t *direntry, off_t length) { off_t clustersize; off_t remaining; uint32_t writetime; int32_t lastcluster; int32_t cluster; int ret; /* Get start cluster of the file to truncate */ lastcluster = ((uint32_t)DIR_GETFSTCLUSTHI(direntry) << 16) | DIR_GETFSTCLUSTLO(direntry); /* Set the file size to the new length. */ DIR_PUTFILESIZE(direntry, length); /* Set the ARCHIVE attribute and update the write time */ DIR_PUTATTRIBUTES(direntry, FATATTR_ARCHIVE); writetime = fat_systime2fattime(); DIR_PUTWRTTIME(direntry, writetime & 0xffff); DIR_PUTWRTDATE(direntry, writetime >> 16); /* This sector needs to be written back to disk eventually */ fs->fs_dirty = true; /* Now find the cluster change to be removed. Start with the cluster * after the current one (which we know contains data). */ cluster = fat_getcluster(fs, lastcluster); if (cluster < 0) { return cluster; } clustersize = fs->fs_fatsecperclus * fs->fs_hwsectorsize; remaining = length; while (cluster >= 2 && cluster < fs->fs_nclusters) { /* Will there be data in the next cluster after the shrinkage? */ if (remaining <= clustersize) { /* No.. then nullify next cluster -- removing it from the * chain. */ ret = fat_putcluster(fs, lastcluster, 0); if (ret < 0) { return ret; } /* Then free the remainder of the chain */ ret = fat_removechain(fs, cluster); if (ret < 0) { return ret; } /* Setup FSINFO to reuse the removed cluster next */ fs->fs_fsinextfree = cluster - 1; break; } /* Then set up to remove the next cluster */ lastcluster = cluster; cluster = fat_getcluster(fs, cluster); if (cluster < 0) { return cluster; } remaining -= clustersize; } return OK; } /**************************************************************************** * Name: fat_dirextend * * Description: * Zero-extend the length of a regular file to 'length'. * ****************************************************************************/ int fat_dirextend(FAR struct fat_mountpt_s *fs, FAR struct fat_file_s *ff, off_t length) { int32_t cluster; off_t remaining; off_t pos; unsigned int zerosize; int sectndx; int ret; /* We are extending the file. This is essentially the same as a write * except that (1) we write zeros and (2) we don't update the file * position. */ pos = ff->ff_size; /* Get the first sector to write to. */ if (!ff->ff_currentsector) { /* Has the starting cluster been defined? */ if (ff->ff_startcluster == 0) { /* No.. we have to create a new cluster chain */ ff->ff_startcluster = fat_createchain(fs); ff->ff_currentcluster = ff->ff_startcluster; ff->ff_sectorsincluster = fs->fs_fatsecperclus; } /* The current sector can then be determined from the current cluster * and the file offset. */ ret = fat_currentsector(fs, ff, pos); if (ret < 0) { return ret; } } /* Loop until either (1) the file has been fully extended with zeroed data * or (2) an error occurs. We assume we start with the current sector in * cache (ff_currentsector) */ sectndx = pos & SEC_NDXMASK(fs); remaining = length - pos; while (remaining > 0) { /* Check if the current write stream has incremented to the next * cluster boundary */ if (ff->ff_sectorsincluster < 1) { /* Extend the current cluster by one (unless lseek was used to * move the file position back from the end of the file) */ cluster = fat_extendchain(fs, ff->ff_currentcluster); /* Verify the cluster number */ if (cluster < 0) { return (int)cluster; } else if (cluster < 2 || cluster >= fs->fs_nclusters) { return -ENOSPC; } /* Setup to zero the first sector from the new cluster */ ff->ff_currentcluster = cluster; ff->ff_sectorsincluster = fs->fs_fatsecperclus; ff->ff_currentsector = fat_cluster2sector(fs, cluster); } /* Decide whether we are performing a read-modify-write * operation, in which case we have to read the existing sector * into the buffer first. * * There are two cases where we can avoid this read: * * - If we are performing a whole-sector clear that was rejected * by fat_hwwrite(), i.e. sectndx == 0 and remaining >= sector size. * * - If the clear is aligned to the beginning of the sector and * extends beyond the end of the file, i.e. sectndx == 0 and * file pos + remaining >= file size. */ if (sectndx == 0 && (remaining >= fs->fs_hwsectorsize || (pos + remaining) >= ff->ff_size)) { /* Flush unwritten data in the sector cache. */ ret = fat_ffcacheflush(fs, ff); if (ret < 0) { return ret; } /* Now mark the clean cache buffer as the current sector. */ ff->ff_cachesector = ff->ff_currentsector; } else { /* Read the current sector into memory (perhaps first flushing the * old, dirty sector to disk). */ ret = fat_ffcacheread(fs, ff, ff->ff_currentsector); if (ret < 0) { return ret; } } /* Copy the requested part of the sector from the user buffer */ zerosize = fs->fs_hwsectorsize - sectndx; if (zerosize > remaining) { /* We will not zero to the end of the sector. */ zerosize = remaining; } else { /* We will zero to the end of the buffer (or beyond). Bump up * the current sector number (actually the next sector number). */ ff->ff_sectorsincluster--; ff->ff_currentsector++; } /* Zero the data into the cached sector and make sure that the cached * sector is marked "dirty" so that it will be written back. */ memset(&ff->ff_buffer[sectndx], 0, zerosize); ff->ff_bflags |= (FFBUFF_DIRTY | FFBUFF_VALID | FFBUFF_MODIFIED); /* Set up for the next sector */ pos += zerosize; remaining -= zerosize; sectndx = pos & SEC_NDXMASK(fs); } /* The truncation has completed without error. Update the file size */ ff->ff_size = length; return OK; } /**************************************************************************** * Name: fat_fscacheflush * * Description: * Flush any dirty sector if fs_buffer as necessary * ****************************************************************************/ int fat_fscacheflush(struct fat_mountpt_s *fs) { int ret; /* Check if the fs_buffer is dirty. In this case, we will write back the * contents of fs_buffer. */ if (fs->fs_dirty) { /* Write the dirty sector */ ret = fat_hwwrite(fs, fs->fs_buffer, fs->fs_currentsector, 1); if (ret < 0) { return ret; } /* Does the sector lie in the FAT region? */ if (fs->fs_currentsector >= fs->fs_fatbase && fs->fs_currentsector < fs->fs_fatbase + fs->fs_nfatsects) { int i; /* Yes, then make the change in the FAT copy as well */ for (i = fs->fs_fatnumfats; i >= 2; i--) { fs->fs_currentsector += fs->fs_nfatsects; ret = fat_hwwrite(fs, fs->fs_buffer, fs->fs_currentsector, 1); if (ret < 0) { return ret; } } } /* No longer dirty */ fs->fs_dirty = false; } return OK; } /**************************************************************************** * Name: fat_fscacheread * * Description: * Read the specified sector into the sector cache, flushing any existing * dirty sectors as necessary. * ****************************************************************************/ int fat_fscacheread(struct fat_mountpt_s *fs, off_t sector) { int ret; /* fs->fs_currentsector holds the current sector that is buffered in * fs->fs_buffer. If the requested sector is the same as this sector, then * we do nothing. Otherwise, we will have to read the new sector. */ if (fs->fs_currentsector != sector) { /* We will need to read the new sector. First, flush the cached * sector if it is dirty. */ ret = fat_fscacheflush(fs); if (ret < 0) { return ret; } /* Then read the specified sector into the cache */ ret = fat_hwread(fs, fs->fs_buffer, sector, 1); if (ret < 0) { return ret; } /* Update the cached sector number */ fs->fs_currentsector = sector; } return OK; } /**************************************************************************** * Name: fat_ffcacheflush * * Description: * Flush any dirty sectors as necessary * ****************************************************************************/ int fat_ffcacheflush(struct fat_mountpt_s *fs, struct fat_file_s *ff) { int ret; /* Check if the ff_buffer is dirty. In this case, we will write back the * contents of ff_buffer. */ if (ff->ff_cachesector && (ff->ff_bflags & (FFBUFF_DIRTY | FFBUFF_VALID)) == (FFBUFF_DIRTY | FFBUFF_VALID)) { /* Write the dirty sector */ ret = fat_hwwrite(fs, ff->ff_buffer, ff->ff_cachesector, 1); if (ret < 0) { return ret; } /* No longer dirty, but still valid */ ff->ff_bflags &= ~FFBUFF_DIRTY; } return OK; } /**************************************************************************** * Name: fat_ffcacheread * * Description: * Read the specified sector into the sector cache, flushing any existing * dirty sectors as necessary. * ****************************************************************************/ int fat_ffcacheread(struct fat_mountpt_s *fs, struct fat_file_s *ff, off_t sector) { int ret; /* ff->ff_cachesector holds the current sector that is buffered in * ff->ff_buffer. If the requested sector is the same as this sector, then * we do nothing. Otherwise, we will have to read the new sector. */ if (ff->ff_cachesector != sector || (ff->ff_bflags & FFBUFF_VALID) == 0) { /* We will need to read the new sector. First, flush the cached * sector if it is dirty. */ ret = fat_ffcacheflush(fs, ff); if (ret < 0) { return ret; } /* Then read the specified sector into the cache */ ret = fat_hwread(fs, ff->ff_buffer, sector, 1); if (ret < 0) { return ret; } /* Update the cached sector number */ ff->ff_cachesector = sector; ff->ff_bflags |= FFBUFF_VALID; } return OK; } /**************************************************************************** * Name: fat_ffcacheread * * Description: * Invalidate the current file buffer contents * ****************************************************************************/ int fat_ffcacheinvalidate(struct fat_mountpt_s *fs, struct fat_file_s *ff) { int ret; /* Is there anything valid in the buffer now? */ if ((ff->ff_bflags & FFBUFF_VALID) != 0) { /* We will invalidate the buffered sector */ ret = fat_ffcacheflush(fs, ff); if (ret < 0) { return ret; } /* Then discard the current cache contents */ ff->ff_bflags &= ~FFBUFF_VALID; ff->ff_cachesector = 0; } return OK; } /**************************************************************************** * Name: fat_updatefsinfo * * Description: * Flush everything buffered for the mountpoint and update the FSINFO * sector, if appropriate * ****************************************************************************/ int fat_updatefsinfo(struct fat_mountpt_s *fs) { int ret; /* Flush the fs_buffer if it is dirty */ ret = fat_fscacheflush(fs); if (ret == OK) { /* The FSINFO sector only has to be update for the case of a FAT32 file * system. Check if the file system type.. If this is a FAT32 file * system then the fs_fsidirty flag will indicate if the FSINFO sector * needs to be re-written. */ if (fs->fs_type == FSTYPE_FAT32 && fs->fs_fsidirty) { /* Create an image of the FSINFO sector in the fs_buffer */ memset(fs->fs_buffer, 0, fs->fs_hwsectorsize); FSI_PUTLEADSIG(fs->fs_buffer, 0x41615252); FSI_PUTSTRUCTSIG(fs->fs_buffer, 0x61417272); FSI_PUTFREECOUNT(fs->fs_buffer, fs->fs_fsifreecount); FSI_PUTNXTFREE(fs->fs_buffer, fs->fs_fsinextfree); FSI_PUTTRAILSIG(fs->fs_buffer, BOOT_SIGNATURE32); /* Then flush this to disk */ fs->fs_currentsector = fs->fs_fsinfo; fs->fs_dirty = true; ret = fat_fscacheflush(fs); /* No longer dirty */ fs->fs_fsidirty = false; } } return ret; } /**************************************************************************** * Name: fat_computefreeclusters * * Description: * Compute the number of free clusters from scratch * ****************************************************************************/ int fat_computefreeclusters(struct fat_mountpt_s *fs) { /* We have to count the number of free clusters */ uint32_t nfreeclusters = 0; if (fs->fs_type == FSTYPE_FAT12) { off_t sector; /* Examine every cluster in the fat */ for (sector = 2; sector < fs->fs_nclusters; sector++) { /* If the cluster is unassigned, then increment the count of free * clusters */ if ((uint16_t)fat_getcluster(fs, sector) == 0) { nfreeclusters++; } } } else { unsigned int cluster; off_t fatsector; unsigned int offset; int ret; fatsector = fs->fs_fatbase; offset = fs->fs_hwsectorsize; /* Examine each cluster in the fat */ for (cluster = fs->fs_nclusters; cluster > 0; cluster--) { /* If we are starting a new sector, then read the new sector in * fs_buffer */ if (offset >= fs->fs_hwsectorsize) { ret = fat_fscacheread(fs, fatsector); if (ret < 0) { return ret; } /* Reset the offset to the next FAT entry. * Increment the sector number to read next time around. */ offset = 0; fatsector++; } /* FAT16 and FAT32 differ only on the size of each cluster start * sector number in the FAT. */ if (fs->fs_type == FSTYPE_FAT16) { if (FAT_GETFAT16(fs->fs_buffer, offset) == 0) { nfreeclusters++; } offset += 2; } else { if (FAT_GETFAT32(fs->fs_buffer, offset) == 0) { nfreeclusters++; } offset += 4; } } } fs->fs_fsifreecount = nfreeclusters; if (fs->fs_type == FSTYPE_FAT32) { fs->fs_fsidirty = true; } return OK; } /**************************************************************************** * Name: fat_nfreeclusters * * Description: * Get the number of free clusters * ****************************************************************************/ int fat_nfreeclusters(struct fat_mountpt_s *fs, fsblkcnt_t *pfreeclusters) { /* If number of the first free cluster is valid, then just return that * value. */ if (fs->fs_fsifreecount <= fs->fs_nclusters - 2) { *pfreeclusters = fs->fs_fsifreecount; return OK; } /* Otherwise, we will have to compute the number of free clusters */ int ret = fat_computefreeclusters(fs); if (ret == OK) { *pfreeclusters = fs->fs_fsifreecount; } return ret; } /**************************************************************************** * Name: fat_currentsector * * Description: * Given the file position, set the correct current sector to access. * ****************************************************************************/ int fat_currentsector(struct fat_mountpt_s *fs, struct fat_file_s *ff, off_t position) { int sectoroffset; off_t cluster_start_sector; if (position <= ff->ff_size) { /* sectoroffset is the sector number offset into the current cluster */ sectoroffset = SEC_NSECTORS(fs, position) & CLUS_NDXMASK(fs); /* The current sector is the first sector of the cluster plus * the sector offset */ cluster_start_sector = fat_cluster2sector(fs, ff->ff_currentcluster); if (cluster_start_sector < 0) { return cluster_start_sector; } ff->ff_currentsector = cluster_start_sector + sectoroffset; /* The remainder is the number of sectors left in the cluster to be * read/written */ ff->ff_sectorsincluster = fs->fs_fatsecperclus - sectoroffset; finfo("position=%" PRIdOFF " currentsector=%" PRIdOFF " sectorsincluster=%d\n", position, ff->ff_currentsector, ff->ff_sectorsincluster); return OK; } /* The position does not lie within the file */ return -ENOSPC; }