Simulate flash filesystem using RAM memory
You must be root to start this driver.|
[-a] [-b priority]
[-E] [-f verifylevel] [-i arrayindex[,partindex]]
[-l] [-m mountover]
[-p backgroundpercent[,superlimit]] [-R] [-r]
[-t threads] [-u update] [-V] [-v]
MIPS, PowerPC, x86, SH, and ARM
- 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.
- Don't daemonize.
If the driver detects a corrupt filesystem, the exit status is that
filesystem's partition number plus 1.
- -f verifylevel
- Simulate flash verify; only provided for syntax
compatibility with real flash hardware (default=0, 0=none, write=1, erase=2,
- -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 a file system that are
formatted with an empty (i.e. flashctl -p/dev/fs0p0 -e -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space) and, optionally, the superseded extent limit before reclaim.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.
The arguments are:
- Physical base address of the flash part. This value is board-specific.
For the devf-ram utility, the base argument carries a
- Allocate system memory.
- Use the exact physical address. You must exercise caution here. See the caveats below.
- 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 simulated flash chip multiplied by the interleave.
This value must be a power of 2 (1, 2, 4, or 8).
- The number of simulated flash chips arranged on the data bus.
This value must be a power of 2 (1, 2, 4, or 8).
You can specify the base physical address, sizes, and offset
in octal (0777), hexadecimal (0x1ff), 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
|| On ARM targets, devf-ram can't resize the shared object
If you need to restart devf-ram with a new size, first unlink
the old shared object:
- -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
in the entry for
- -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-ram manager simulates flash filesystem in RAM using the
following default filenames (the ID, n, appended to
be changed via the -i option):
- 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.
Start devf-ram with a 16 MB partition.
Start devf-ram and automatically mount the flash filesystem
partitions, with an initial fault recovery process, most POSIX semantics
enabled and background reclaim at priority 5 (default size: 1 MB):
devf-ram -r -u2 -b5 &
Create a 32 MB flash partition, allocated from system RAM, with a 64 KB unit
devf-ram -s0,32m,,,64k -v -r
Create a 128 MB flash partition in system RAM, with large block sizes (to
devf-ram -s0,128m,,,512k -v -r
Create a 4 MB partition from system RAM:
devf-ram -s0,4m,,,64k -v -r
||You must format and erase a
devf-ram partition before you can mount the flash filesystem. See
the caveats below.
||If you specify a block size in your buildfile for DRAM-based flash filesystems,
limit the size to the default, which is 64 KB.|
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.
Don't try to create a devf-ram partition at the address of a real flash memory.
You may get an error message: Unable to properly identify any flash
Don't try to create a devf-ram partition (e.g. using nonzero value for
base argument) at the address of physical memory that is in use.
It may destroy applications and crash the operating system.
The only use for specifying such nonzero base is to create a
flash filesystem for board specific memory (e.g. SRAM).
You must format and erase a
devf-ram partition before you can mount the flash filesystem. e.g.
flashctl -p /dev/fs0p0 -e -f -m
If there's insufficient RAM, when you try to create an nM size
partition with -s0 option, the
devf-ram driver returns without an error message.
The partition isn't created.
in the Working With Filesystems chapter of the User's Guide