Generic flash filesystem
You must be root to start this driver.|
[-a] [-b priority] [-d log_method] [-E] [-e auto]
[-f verifylevel] [-i arrayindex[,partindex]]
[-l] [-m mountover
[-p backgroundpercent[,superlimit]] [-R] [-r]
[-t threads] [-u update] [-V] [-v]
Most flash devices
- Don't automount filesystem partitions present on the media.
If you specify both the -a and -R options,
the driver ignores the -R option.
- -b priority
- Enable background reclaim at the specified priority.
By default, background reclamation is disabled.
- -d log_method
- Control the logging from the flash driver.
The possible values for log_method are:
- 0 — log to stdout (the default).
- 1 — log to
- 2 — log to both stdout and slogger.
- Don't daemonize.
If the driver detects a corrupt filesystem, the exit status is that
filesystem's partition number plus 1.
- -e auto
- Only enumerate the flash partitions, instead of doing a full scan
The flash driver automounts all partitions with a partition number
less than or equal to auto.
For example, assume we have a flash layout as follows:
- /dev/fs0p0 — raw
- /dev/fs0p1 — formatted
- /dev/fs0p2 — formatted
- /dev/fs0p3 — formatted
If you start the driver with -e 1, the driver creates all the
raw entries in /dev, but mounts only
/dev/fs0p1 (/dev/fs0p0 is raw, so it's never
mounted, regardless of the -e option)
- -f verifylevel
- Enable flash verify. (default=0, 0=none, write=1, erase=2, all=3)
- -i arrayindex[,partindex]
- Starting socket index and first partition index;
0 ≥ index ≥15. The default is 0,0.
Use this to give multiple drivers unique IDs.
The -i option is just a suggestion for the resource
database manager; the selected indexes can be larger.
- List the available flash databases and exit.
- -m mountover
- Override the mountpoints assigned to the file system that are formatted
with an empty (i.e. flashctl -p/dev/fs0p0 -f -n "") mountpoint. The mountover
argument can include two
%X format specifiers (like those for printf())
that are replaced by the socket index and the partition index.
|| The -m option doesn't override a mountpoint specified with
- -p backgroundpercent[,superlimit]
- Set the background-reclaim percentage trigger (stale space over free
space) and, optionally, the superseded extent limit before reclaim.
The default is 100,16.
- Mount any automount filesystems as read-only.
This option doesn't affect raw partition mounts, and it has an effect
only at startup and initialization.
Any subsequent mounting (with either
ignores the -R option.
If you also specify the -a option, the driver ignores the
- Enable fault recovery for dirty extents, dangling extents, and partial
|| You should always specify the -r option unless you're
trying to debug an issue concerning flash corruption.
If you don't specify -r, and a power failure occurs,
the following can happen:
- You can waste space.
If an erasure was happening when the power was cut off,
there will be some “dangling” extents (i.e. marked for
deletion, but not actually deleted).
If you specify the -vv option, the driver prints
dangle for every dangling extent found.
These extents will continue to occupy space forever, until they're
Using the -r option will cause them to be reclaimed.
- The system may be marked as read-only.
If the driver detects an error in the structure of the filesystem,
and you haven't specified the
-r option, the driver marks the partition as read-only,
so that it can't be further damaged.
- If a reclaim operation is interrupted by a power loss, the spare block
may be unusable.
In this case, if you specify the -vv option, the driver prints
partial to the console.
The partition is still read-write, but reclaims are turned off;
if you continue to overwrite files, you'll eventually fill the
filesystem with stale data.
- -s base[,wsize[,aoffset[,asize[,usize[,bwidth[,ileave]]]]]]
- Set socket options, normally the base physical address, window size,
array offset, array size, unit size, bus width, and interleave. The format is left flexible
for socket services with customized drivers. This option must be specified.
The arguments are:
- Physical base address of the flash part. This value is board-specific.
- Size of the physically contiguous flash part.
- For SRAM, the offset from the base address to the start of the flash
- For SRAM, the size of the flash array. The default is equal to
- The size of a physical erase sector. For SRAM, this number can be any
power of two. 64 KB should be the minimum, for performance reasons.
- The total width of the data bus, as seen from the microprocessor's
perspective. This is the width of one flash chip multiplied by the
The value must be a power of 2 (1, 2, 4, or 8).
- The number of flash chips arranged on the data bus.
Two 16-bit wide chips used as the upper and lower halves of a 32-bit
databus give an interleave of 2.
This number must be a power of 2 (1, 2, 4, or 8).
You can specify the base physical address, sizes, and offset
in octal (1000), hexadecimal (0x200), or
The sizes must be a power of two, and you can specify them with any of
the following suffixes:
- (nothing) — bytes
- k — kilobytes
- m — megabytes
- -t threads
- The number of threads.
The minimum is 1, the default is 2, and the maximum is 100.
Extra threads increase performance when
background reclaiming is enabled (with the -b option) and
when multiple chips and/or spare blocks are available.
- -u update
- Specify the update level for timestamps.
POSIX specifies that timestamps be kept when you access, create, or
modify a file.
FFSv3 is documented as not supporting the access
timestamp, in order to reduce wear on the hardware.
The values for update are:
- 0 — don't update the modification time for files (the default).
- 1 — update the modification time for files according to
the POSIX rules.
- 2 — update the modification time for files, as well as for
the parent directory.
|| The -u2 option is very, very expensive and will cause many
reclaims because the time updates have to flow right up to the root
directory, so one file update may cause many directory updates.
- Display filesystem and MTD version information, and then exit.
- Be verbose; specify additional v characters for more verbosity.
For more information, see
- -w buffersize
- Write (append) buffer size in bytes. The default
buffersize is 512. Using a larger write-buffer
prevents the creation of very small extents, reducing overhead.
If buffersize is 0, appending is disabled.
The devf-generic manager provides Flash filesystem
support for any standard flash device. Typically, all you need to do is to pass
the address and size using the -s option. The manager should detect the
For information on creating a custom variant of devf-generic
for your embedded system, see the
Customizing the Flash Filesystem
chapter of Building Embedded Systems
The default filenames are as follows (you can use the -i option to
change the ID, n, appended to /dev/fs):
- Default mountpoint for socket n.
- Raw access for socket n, partition 0.
- Flash filesystem mountpoint for socket n, partition 0 with
You can specify the mountpoint above with the
mount attribute of the
command, and override it with the
-n option to
By default, it's /fsnp0.
||If you erase a raw partition or the raw array (socket),
you might erase any boot monitor,
BIOS, or other data installed by the manufacturer.
Check the documentation for the board.|
The driver probes the hardware to determine its block size.
If you need to know the block size, you can:
- Look in the documentation for the hardware.
- Start the driver in verbose mode by specifying the -v option.
In the output, U: indicates the number of units (also known as
blocks or sectors),
and S: indicates the block size.
Both numbers are in hexadecimal.
- Start the driver, and then run
specifying the -i option.
If you specify the -v option, a devf-* driver provides
some useful information.
This section describes the output that you get if you specify -vvv;
at higher levels of verbosity, the output also includes messages about the
use of malloc() and free(), but these aren't likely
to be useful to you.
The output starts with something like this:
Flash Development Library - HEAD
Build: Jan 15 2010 13:00:00
MTD Build: Jan 15 2010, 13:25:55
These lines identify the source branch of the build, as well as the
build times for libfs-flash3.a and
The rest of the messages that the driver prints are variable; messages are
printed as the driver discovers things of interest.
The general format of a message is
(devf tN::function:line) Message string
where tN is the thread printing the message,
function is the function emitting the message, and
line is the line number that emitted the message.
The standard messages include the following:
- (devf t1::f3s_skt_attach:109) fs0 socket RAM (flash simulation)
- The flash driver located a flash socket, number zero (fs0).
This message also indicates that the hardware identification succeeded.
- (devf t1::f3s_flash_probe:248) chip total = 1, bus_width = 8, interleave = 2
- After identifying the hardware, the driver prints the geometry.
The chip total is the number of contiguous chips.
The bus width is the size of the data bus, in bytes.
The interleave is the number of physical chips sharing
the data bus (high and low halves of the data bus, for example).
This particular example indicates that there are two physical chips
sharing a 64-bit data bus.
- (devf t1::f3s_skt_attach:135) fs0 array SRAM U: 80 S: 020000
- The flash driver has allocated the flash array
(i.e. the storage media) of type SRAM, with 0x80 hardware sectors,
and a sector size of 0x020000 bytes.
- (devf t1::f3s_recover_boot:248) fs0p0 boot P U: 80
- The filesystem is now scanning for partitions.
It has found a boot header, and has named the partition
/dev/fs0p0. The boot signature is located on physical
block 0, and the partition has 0x80 sectors (called “units” in
- (devf t1::f3s_recover_reclaim:989) fs0p0 spare P[7F]
- The second phase of the startup scan is processing
/dev/fs0p0, and has found a spare block.
The spare block is located on physical sector 0x7F.
- (devf t3::f3s_table_find:66) fs0p1 raw U: 09
- A region of flash was found that isn't formatted.
The region is given the name /dev/fs0p1; its size is 0x09
Start devf-generic and automatically mount the flash filesystem
partitions at the base address 0xFF000 with a window size of 16 megabytes,
with an initial fault recovery process, most POSIX semantics
enabled and background reclaim at priority 5:
devf-generic -s 0xFF000,16M -r -u2 -b5 &
Create a 32 MB flash partition, with a 64 KB unit (sector) size:
devf-generic -s0,32m,,,64k -v -r
Create a 128 MB flash partition, with large block sizes (to
devf-generic -s0,128m,,,512k -v -r
Create a 4 MB partition:
devf-generic -s0,4m,,,64k -v -r
Create a 16 MB flash partition, from a given physical address, with a 128 KB
unit size, and a 16-bit wide data bus:
devf-generic -s0xa4000000,16m,,,128k,2 -v -r
Create a 16 MB flash partition, from a given physical address, with a 256 KB
unit size, and a 32-bit-wide data bus, with an interleave of two:
devf-generic -s0,16m,,,256k,4,2 -v -r
You must specify the -s option when using this driver.
Although the Flash filesystem supports most POSIX semantics, some
functionality isn't implemented in order to keep the driver simple and
efficient. The unsupported POSIX semantics include:
- Hard links, and everything related to hard links (the
. and .. directories don't exist,
struct stat's nlink member is hard-coded,
of directories returns ENOTSUP).
- Access times aren't updated on the media; they're set to
the modification time.
QNX Neutrino flash filesystem version 3 no longer
provides built-in decompression.
The flash filesystem's decompression functionality has moved into the
resource manager. You should now use the deflate utility
to compress files.
Performance might be slow when multiple writers are writing randomly
to a shared file or to a shared directory (e.g. using unlink or
In these cases,
the offset pointers have to be rewound for every access.
There's no performance penalty when appending to a file, or when
creating files with open(O_CREAT),
mkdir, mknod, or link.
in the Working With Filesystems chapter of the User's Guide
Customizing the Flash Filesystem
chapter of Building Embedded Systems