216 lines
7.0 KiB
ReStructuredText
216 lines
7.0 KiB
ReStructuredText
=================
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NuttX File System
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=================
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**Overview**. NuttX includes an optional, scalable file system.
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This file-system may be omitted altogether; NuttX does not depend
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on the presence of any file system.
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**Pseudo Root File System**. A simple *in-memory*, *pseudo* file
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system can be enabled by default. This is an *in-memory* file
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system because it does not require any storage medium or block
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driver support. Rather, file system contents are generated
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on-the-fly as referenced via standard file system operations
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(open, close, read, write, etc.). In this sense, the file system
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is *pseudo* file system (in the same sense that the Linux
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``/proc`` file system is also referred to as a pseudo file
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system).
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Any user supplied data or logic can be accessed via the
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pseudo-file system. Built in support is provided for character and
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block `drivers <#DeviceDrivers>`__ in the ``/dev`` pseudo file
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system directory.
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**Mounted File Systems** The simple in-memory file system can be
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extended my mounting block devices that provide access to true
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file systems backed up via some mass storage device. NuttX
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supports the standard ``mount()`` command that allows a block
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driver to be bound to a mountpoint within the pseudo file system
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and to a file system. At present, NuttX supports the standard VFAT
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and ROMFS file systems, a special, wear-leveling NuttX FLASH File
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System (NXFFS), as well as a Network File System client (NFS
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version 3, UDP).
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**Comparison to Linux** From a programming perspective, the NuttX
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file system appears very similar to a Linux file system. However,
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there is a fundamental difference: The NuttX root file system is a
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pseudo file system and true file systems may be mounted in the
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pseudo file system. In the typical Linux installation by
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comparison, the Linux root file system is a true file system and
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pseudo file systems may be mounted in the true, root file system.
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The approach selected by NuttX is intended to support greater
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scalability from the very tiny platform to the moderate platform.
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Partition Table
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===============
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Text based Partition Table
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----------------------------------
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**Summary**
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TXTABLE - A text based partition table stored in last eraseblock
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(or in romdisk for backup).
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1. The 1st line must be "Magic+Version", current is "TXTABLE0".
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#. The 2nd and remaining lines are partition entries(min: one)
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in format: "%s %zx %zx"(means name, size and offset (byte)(in hex)).
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#. Size or offset can be default zero(means zero(for 1st entry) or
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caculate(for others)), and will be caculated by the parser refs to previous
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and next entries.
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#. The last eraseblock will be registered as pseudo partition named "txtable".
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If the last eraseblock included by the last real partition, it will be
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excluded from.
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To avoid problems of PTABLE: In case of multiple NuttX binary,
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partition table maybe out of sync.
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And it's easier:
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1. Text format with simple rules(name + size + offset).
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#. Size or offset can be default(caculated refs to previous
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and next entries).
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#. Support backup table(eg. /etc/txtable.txt in ROMFS)
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Size / Offset can be automatically calculated, case:
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1. The offset of the first entry is zero, and the offset of other entries
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is zero: automatic calculation;
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#. The size of the last entry is zero: fill to the end of the entire Flash
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(keep the last eraseblock); the size of other entries is zero:
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automatically calculated(next.offset - current.offset);
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#. Typical case 1: The size of all entries is
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zero (calculated automatically), and the offset is non-zero;
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#. Typical case 2: The size and offset of a certain entry are all zero,
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but the size and offset of two adjacent entries are all non-zero;
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**Examples**
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Both size and offset of "partition6" are zero,
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gap exists between "partition7" and "data",
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and not reserve last eraseblock.
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* txtable.txt
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::
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TXTABLE0
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partition1 0x6C000 0x4000
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partition2 0x10000 0x70000
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partition3 0x80000 0x80000
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partition4 0x80000 0x100000
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partition5 0x280000 0x180000
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partition6 0 0
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partition7 0x10000 0x480000
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data 0 0x500000
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* Parsed
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| Reserved last eraseblock, and gap between partition7 and data is kept.
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| Format: name, offset, size
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::
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/dev/partition1 offset 0x00004000, size 0x0006c000
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/dev/partition2 offset 0x00070000, size 0x00010000
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/dev/partition3 offset 0x00080000, size 0x00080000
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/dev/partition4 offset 0x00100000, size 0x00080000
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/dev/partition5 offset 0x00180000, size 0x00280000
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/dev/partition6 offset 0x00400000, size 0x00080000
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/dev/partition7 offset 0x00480000, size 0x00010000
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/dev/data offset 0x00500000, size 0x00aff000
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/dev/txtable offset 0x00fff000, size 0x00001000
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More than one not set size or offset
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* txtable.txt
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::
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TXTABLE0
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partition1 0 0x4000
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partition2 0 0x70000
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partition3 0 0x80000
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partition4 0x80000 0x100000
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partition5 0x280000 0
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partition6 0 0
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partition7 0x10000 0x480000
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data 0 0x500000
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* Parsed
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| Size of partition[2,3,4,6] and data are caculated, and gap between
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partition7 and data is kept.
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::
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/dev/partition1 offset 0x00004000, size 0x0006c000
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/dev/partition2 offset 0x00070000, size 0x00010000
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/dev/partition3 offset 0x00080000, size 0x00080000
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/dev/partition4 offset 0x00100000, size 0x00080000
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/dev/partition5 offset 0x00180000, size 0x00280000
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/dev/partition6 offset 0x00400000, size 0x00080000
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/dev/partition7 offset 0x00480000, size 0x00010000
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/dev/data offset 0x00500000, size 0x00aff000
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/dev/txtable offset 0x00fff000, size 0x00001000
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Only one partition entry, and size not spec
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* txtable.txt
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::
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TXTABLE0
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partition1 0x0 0x4000
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* Parsed
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| The last eraseblock was kept, and size is correct.
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::
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/dev/partition1 offset 0x00004000, size 0x00ffb000
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/dev/txtable offset 0x00fff000, size 0x00001000
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Blank line && New line delim
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* txtable.txt
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| New line: CR + LF / LF.
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| Additional char/string after "%s %zx %zx".
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::
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TXTABLE0
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partition1 0x6C000 0x4000
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partition2 0 0x70000
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partition3 0 0x80000
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partition4 0 0x100000
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partition5 0x280000 0x180000
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partition6 0x80000 0x400000 # String between "%s %zx %zx" and "LF" will be ignored.
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partition7 0x10000 0x480000 # Comments: This is the 7th partition.
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data 0 0x500000
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EOF
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* Parsed
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| Blank lines are ignored, and new line of both "LF" or "CRLF" are parsed.
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String between "%s %zx %zx" and "LF" will be ignored(eg. CR, or some comments).
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::
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/dev/partition1 offset 0x00004000, size 0x0006c000
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/dev/partition2 offset 0x00070000, size 0x00010000
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/dev/partition3 offset 0x00080000, size 0x00080000
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/dev/partition4 offset 0x00100000, size 0x00080000
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/dev/partition5 offset 0x00180000, size 0x00280000
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/dev/partition6 offset 0x00400000, size 0x00080000
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/dev/partition7 offset 0x00480000, size 0x00010000
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/dev/data offset 0x00500000, size 0x00aff000
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/dev/txtable offset 0x00fff000, size 0x00001000
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