/****************************************************************************
* mm/shm/shmget.c
*
* Copyright (C) 2014 Gregory Nutt. All rights reserved.
* Author: Gregory Nutt <gnutt@nuttx.org>
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
* 3. Neither the name NuttX nor the names of its contributors may be
* used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*
****************************************************************************/
/****************************************************************************
* Included Files
****************************************************************************/
#include <nuttx/config.h>
#include <sys/shm.h>
#include <sys/ipc.h>
#include <unistd.h>
#include <semaphore.h>
#include <string.h>
#include <errno.h>
#include <nuttx/pgalloc.h>
#include <nuttx/mm/shm.h>
#include "shm/shm.h"
#ifdef CONFIG_MM_SHM
/****************************************************************************
* Private Functions
****************************************************************************/
/****************************************************************************
* Name: shm_find
*
* Description:
* Find the shared memory region with matching key
*
* Input parameters:
* key - The value that uniquely identifies a shared memory region.
*
* Returned value:
* On success, an index in the range of 0 to CONFIG_ARCH_SHM_MAXREGIONS-1
* is returned to identify the matching region; -ENOENT is returned on
* failure.
*
****************************************************************************/
static int shm_find(key_t key)
{
int i;
for (i = 0; i < CONFIG_ARCH_SHM_MAXREGIONS; i++)
{
if (g_shminfo.si_region[i].sr_key == key)
{
return i;
}
}
return -ENOENT;
}
/****************************************************************************
* Name: shm_reserve
*
* Description:
* Allocate an unused shared memory region. That is one with a key of -1
*
* Input parameters:
* None
*
* Returned value:
* On success, an index in the range of 0 to CONFIG_ARCH_SHM_MAXREGIONS-1
* is returned to identify the matching region; -ENOSPC is returned on
* failure.
*
****************************************************************************/
static int shm_reserve(key_t key, int shmflg)
{
FAR struct shm_region_s *region;
int i;
for (i = 0; i < CONFIG_ARCH_SHM_MAXREGIONS; i++)
{
/* Is this region in use? */
region = &g_shminfo.si_region[i];
if (region->sr_flags == SRFLAG_AVAILABLE)
{
/* No... reserve it for the caller now */
memset(region, 0, sizeof(struct shm_region_s));
region->sr_key = key;
region->sr_flags = SRFLAG_INUSE;
sem_init(®ion->sr_sem, 0, 1);
/* Set the low-order nine bits of shm_perm.mode to the low-order
* nine bits of shmflg.
*/
region->sr_ds.shm_perm.mode = shmflg & IPC_MODE;
/* The value of shm_segsz is left equal to zero for now because no
* memory has yet been allocated.
*
* The values of shm_lpid, shm_nattch, shm_atime, and shm_dtime are
* set equal to 0.
*/
/* The value of shm_ctime is set equal to the current time. */
region->sr_ds.shm_ctime = time(NULL);
return i;
}
}
return -ENOSPC;
}
/****************************************************************************
* Name: shm_extend
*
* Description:
* Extend the size of a memory regions by allocating physical pages as
* necessary
*
* Input parameters:
* shmid - The index of the region of interest in the shared memory region
* table.
* size - The new size of the region.
*
* Returned value:
* Zero is returned on success; -ENOMEM is returned on failure.
* (Should a different error be returned if the region is just too big?)
*
****************************************************************************/
static int shm_extend(int shmid, size_t size)
{
FAR struct shm_region_s *region = &g_shminfo.si_region[shmid];
unsigned int pgalloc;
unsigned int pgneeded;
/* This is the number of pages that are needed to satisfy the allocation */
pgneeded = MM_PGALIGNUP(size);
/* This is the number of pages that have already been allocated */
pgalloc = MM_PGALIGNUP(region->sr_ds.shm_segsz);
/* Loop until all pages have been allocated (or something bad happens) */
while (pgalloc < pgneeded && pgalloc < CONFIG_ARCH_SHM_NPAGES)
{
/* Allocate one more physical page */
region->sr_pages[pgalloc] = mm_pgalloc(1);
if (region->sr_pages[pgalloc] == 0)
{
shmerr("ERROR: mm_pgalloc(1) failed\n");
break;
}
/* Increment the number of pages successully allocated */
pgalloc++;
}
/* We get here (1) because all of the pages were successfully, (2) because
* mm_pgalloc() failed, or (3) because any additional pages allocated
* would exceed CONFIG_ARCH_SHM_NPAGES.
*/
if (pgalloc < pgneeded)
{
/* Set the amount memory available which will be less than the
* requested size.
*/
region->sr_ds.shm_segsz = pgalloc << MM_PGSHIFT;
return -ENOMEM;
}
/* Set the new region size and return success */
region->sr_ds.shm_segsz = size;
return OK;
}
/****************************************************************************
* Name: shm_create
*
* Description:
* Create the shared memory region.
*
* Input parameters:
* key - The key that is used to access the unique shared memory
* identifier.
* size - The shared memory region that is created will be at least
* this size in bytes.
* shmflgs - See IPC_* definitions in sys/ipc.h. Only the values
* IPC_PRIVATE or IPC_CREAT are supported.
*
* Returned value:
* Zero is returned on success; A negated errno value is returned on
* failure.
*
****************************************************************************/
static int shm_create(key_t key, size_t size, int shmflg)
{
FAR struct shm_region_s *region;
int shmid;
int ret;
/* Reserve the shared memory region */
ret = shm_reserve(key, shmflg);
if (ret < 0)
{
shmerr("ERROR: shm_reserve failed: %d\n", ret);
return ret;
}
/* Save the shared memory ID */
shmid = ret;
/* Then allocate the physical memory (by extending it from the initial
* size of zero).
*/
ret = shm_reserve(shmid, size);
if (ret < 0)
{
/* Free any partial allocations and unreserve the region */
shm_destroy(shmid);
return ret;
}
/* Save the process ID of the creator */
region = &g_shminfo.si_region[shmid];
region->sr_ds.shm_cpid = getpid();
/* Return the shared memory ID */
return shmid;
}
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Name: shmget
*
* Description:
* The shmget() function will return the shared memory identifier
* associated with key.
*
* A shared memory identifier, associated data structure, and shared
* memory segment of at least size bytes is created for key if one of the
* following is true:
*
* - The argument key is equal to IPC_PRIVATE.
* - The argument key does not already have a shared memory identifier
* associated with it and (shmflg & IPC_CREAT) is non-zero.
*
* Upon creation, the data structure associated with the new shared memory
* identifier will be initialized as follows:
*
* - The low-order nine bits of shm_perm.mode are set equal to the low-
* order nine bits of shmflg.
* - The value of shm_segsz is set equal to the value of size.
* - The values of shm_lpid, shm_nattch, shm_atime, and shm_dtime are
* set equal to 0.
* - The value of shm_ctime is set equal to the current time.
*
* When the shared memory segment is created, it will be initialized with
* all zero values.
*
* Input Parameters:
* key - The key that is used to access the unique shared memory
* identifier.
* size - The shared memory region that is created will be at least
* this size in bytes.
* shmflgs - See IPC_* definitions in sys/ipc.h. Only the values
* IPC_PRIVATE or IPC_CREAT are supported.
*
* Returned Value:
* Upon successful completion, shmget() will return a non-negative
* integer, namely a shared memory identifier; otherwise, it will return
* -1 and set errno to indicate the error.
*
* - EACCES
* A shared memory identifier exists for key but operation permission
* as specified by the low-order nine bits of shmflg would not be
* granted.
* - EEXIST
* A shared memory identifier exists for the argument key but
* (shmflg & IPC_CREAT) && (shmflg & IPC_EXCL) are non-zero.
* - EINVAL
* A shared memory segment is to be created and the value of size is
* less than the system-imposed minimum or greater than the system-
* imposed maximum.
* - EINVAL
* No shared memory segment is to be created and a shared memory
* segment exists for key but the size of the segment associated with
* it is less than size and size is not 0.
* - ENOENT
* A shared memory identifier does not exist for the argument key and
* (shmflg & IPC_CREAT) is 0.
* - ENOMEM
* A shared memory identifier and associated shared memory segment
* will be created, but the amount of available physical memory is
* not sufficient to fill the request.
* - ENOSPC
* A shared memory identifier is to be created, but the system-imposed
* limit on the maximum number of allowed shared memory identifiers
* system-wide would be exceeded.
*
* POSIX Deviations:
* - The values of shm_perm.cuid, shm_perm.uid, shm_perm.cgid, and
* shm_perm.gid should be set equal to the effective user ID and
* effective group ID, respectively, of the calling process.
* The NuttX ipc_perm structure, however, does not support these
* fields because user and group IDs are not yet supported by NuttX.
*
****************************************************************************/
int shmget(key_t key, size_t size, int shmflg)
{
FAR struct shm_region_s *region;
int shmid = -1;
int ret;
/* Check for the special case where the caller doesn't really want shared
* memory (they why do they bother to call us?)
*/
if (key == IPC_PRIVATE)
{
/* Not yet implemented */
ret = -ENOSYS;
goto errout;
}
/* Get exclusive access to the global list of shared memory regions */
ret = sem_wait(&g_shminfo.si_sem);
if (ret >= 0)
{
/* Find the requested memory region */
ret = shm_find(key);
if (ret < 0)
{
/* The memory region does not exist.. create it if IPC_CREAT is
* included in the shmflags.
*/
if ((shmflg & IPC_CREAT) != 0)
{
/* Create the memory region */
ret = shm_create(key, size, shmflg);
if (ret < 0)
{
shmerr("ERROR: shm_create failed: %d\n", ret);
goto errout_with_semaphore;
}
/* Return the shared memory ID */
shmid = ret;
}
else
{
/* Fail with ENOENT */
goto errout_with_semaphore;
}
}
/* The region exists */
else
{
/* Remember the shared memory ID */
shmid = ret;
/* Is the region big enough for the request? */
region = &g_shminfo.si_region[shmid];
if (region->sr_ds.shm_segsz < size)
{
/* We we asked to create the region? If so we can just
* extend it.
*
* REVISIT: We should check the mode bits of the regions
* first
*/
if ((shmflg & IPC_CREAT) != 0)
{
/* Extend the region */
ret = shm_extend(shmid, size);
if (ret < 0)
{
shmerr("ERROR: shm_create failed: %d\n", ret);
goto errout_with_semaphore;
}
}
else
{
/* Fail with EINVAL */
ret = -EINVAL;
goto errout_with_semaphore;
}
}
/* The region is already big enough or else we successfully
* extended the size of the region. If the region was previously
* deleted, but waiting for processes to detach from the region,
* then it is no longer deleted.
*/
region->sr_flags = SRFLAG_INUSE;
}
/* Release our lock on the shared memory region list */
sem_post(&g_shminfo.si_sem);
}
return shmid;
errout_with_semaphore:
sem_post(&g_shminfo.si_sem);
errout:
set_errno(-ret);
return ERROR;
}
#endif /* CONFIG_MM_SHM */