Right now, many users are trying out many different filesystems.
Unfortunately, this can leave partially written filesystems on disk
in various states.
A very common pattern for using embedded filesystems is to attempt
a mount, and on failure, format the storage with the filesystem.
Unfortunately, this simply doesn't work if you try to change the
filesystem being used on a piece of storage. Filesystems don't always
use the same regions of storage, and can leave enough metadata lying
around from old filesystems to trick a different mount into thinking a
valid filesystem exists on disk. The filesystems we have were never
designed to check for malicious modification and can't protect against
arbitrary changes.
That being said, it's caused enough problems for users, so as a
workaround this patch adds a disk erase to the FAT filesystem format.
The most common error happens when you use LittleFS, followed by FAT,
followed again by LittleFS.
No other combination of filesystem usage has shown a similar failure,
but it is possible after extensive filesystem use, so it is still
suggested to force a format of the storage when changing filesystems.
Regression after ChanFS update: Due to parameter changes in the f_mkfs
function, the option to use a separate block for MBR (FDISK) was turned
back on. This should be off as it conflicts with an explicit MBR when
using the MBRBlockDevice.
FATFilesystem declares sector count and size as uint32_t and block
device class arguments are addr and size which is uint64_t
While passing arguments to program/read/write API's of block device,
multiplication of uint32_t*uint32_t was not typecasted properly to
uint64_t which resulted in MSB truncation.
Eg. If block 0x800000 is accessed with block size 0x200, addr to be
passed (0x800000*0x200)0x100000000, but actual address passed was 0x0
which resulted in over-writting the root directory, and hence corrupted
filesystem
The API is as per posix standard, but does not provide stats for file/directory.
Stats buffer (block size, total block count, free block count) is filled for
entire mounted filesystem.
The index field of FATFS_DIR does not encapsulate all the context
required to reposition the directory traversal. ChaN provides
f_rewinddir() but no directory seek, so rewind if necessary then step
through until the desired index is reached.
Some block devices (for example I2C EEPROM) can be erased at the byte
level. These aren't really block devices, but fall under the block
device API. For these devices, the fat filesystem needs to use a lower
bound on the block size. In this case we used 512 bytes is used since
it is already a standard.
This function provides a shortcut to reformatting a mounted filesystem.
Also, since this function is a virtual member of the FileSystem class,
the user does not need to know the underlying filesystem to reformat
the underlying storage.
This is only an issue when multiple fatfss are used simultaneously.
Repeated use of a single fatfs instance (even with different storages)
do not show this issue.
Full support requires path prefixes being applied for every function
that takes a path. Note: this is only required filesystems after the
first mounted filesystem. The first filesystem has no penalty.
Unlike the other disk_ioctl options, GET_SECTOR_SIZE is interpreted
as a 16-bit WORD, instead of a 32-bit DWORD. This caused an unaligned
access error on M0 platforms.
At some point the "mount" parameter for "f_mount" was name "force". This
led to a bit of confusion that ended with the default mount function
never calling block device init.
This is fine, since the block device can be manually initialized, but
a better user experience is where the filesystem initializes the block
device for the user.
This is backwards compatible due to the repeatability of the block
device init functions.
This is necessary for support of block devices with >512 byte
blocks, such as most SPI flash parts.
- Enabled support of up to 4096 byte blocks
- Added support for heap-backed buffers using _FS_HEAPBUF
- Necessary to avoid stack overflows
- Avoids over-aggresive allocations of _MAX_SS
- Enabled _FS_TINY to further reduce memory footprint
- Haven't found a downside for this yet except for possible
thread contention
- Implicit MBR still allowed during mount
- maintains storage compatibility
- Not needed
- MBR utility is not exposed through the FAT filesystem,
so the only used partition was always the first. Omitting
the MBR is functionally equivalent
- Saves a few blocks on storage for MBR + offset
for FAT alignment
- Duplicated with MBRBlockDevice
- The implicit MBR actually prevents nesting a FAT filesystem
in the MBRBlockDevice
The standard is intentionally vague on if filesystems must
have '.' and '..' entries, allowing filesystems to omit this
concept completely:
http://pubs.opengroup.org/onlinepubs/9699919799/functions/readdir.html
However, the '.' and '..' entries are common on FAT filesystems
and in most other filesystems.
This enables '.' and '..' entries in the FAT filesystem.
- Remove write set of functions
- Caused confusion with small benefit
- Trivial to add later
- Remove unused error codes
- Initial expirementation indicates most of these may not be useful
- Trivial to add later
- Removed bd_error_t
- Carries to additional type information, int already carries
sufficient connotation
- Trivial to add later
per @c1728p9, @sg-
- Fixing code formatting errors with astyle tool.
- Replaced use of TOOLCHAIN_xxx macros with compiler emitted macros.
- Added const to BlockDevice::get_xxx_size() member functions.
- Added documentation for FAT filesystem thread support.
- Added documentation for fat_filesystem_set_errno().
- Added documentation clarifying the reasons for errno/stat symbol definitions in retarget.h.
- Removed FAT filesystem from mbed 2 testing.
- Fixed FATMisc.h Copyright (c) 2016 year to 2017 as its a new file.
- Removed #ifndef NDEBUG from HeapBlockDevice.cpp.
- Removed unnecessary todo comment in retarget.cpp.
- renaming FATFileSystemSetErrno() fat_file_system_set_errno.
- changing FATFileSystem::format() to be mount fs internally in function, rather than expecting fs to be mounted.
- requested const char *filename change.
Brendan McDonnell
Martin Kojtal
Christopher Haster
Deepika
Cruz Monrreal II
Martin Kojtal
Colin Hogben
Jimmy Brisson
Kevin Bracey
Simon Hughes