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SubjectRe: request_firmware() hotplug interface, third round.
Hi all,

On Thu, May 15, 2003 at 10:03:24PM +0200, Manuel Estrada Sainz wrote:
> - echo 1 > /sysfs/class/firmware/dev_name/loading
> - cat whatever_fw > /sysfs/class/firmware/dev_name/data
> - echo 0 > /sysfs/class/firmware/dev_name/loading

Why not doing that in open and require firmware data to contain
size information? Good firmware formats contain already size,
checksum and version information. Bad firmware can be wrapped to
get these. It should be made a requirement to contain at least a
size and a checksum.

To handle the big varieties of firmware formats, I would suggest
to either wrap all in user space or define 3 functions per
firmware format like the seq_file support. The thing is very
similiar, except that we read from user space instead of writing.


fw_begin_firmware_store() gets at most a page of data and should
evaluate from this data, how much bytes it still needs from
user space. It will also setup a context and store it.

fw_next_firmware_bytes() will get passed more firmware bytes and
tells us again how much it still need. It will get passed the
context setup by fw_begin_firmware_store().

This function can also abort a download by returning "no bytes
needed anymore" and marking the firmware "invalid" in the
context, which fw_end_firmware_store() will use to return
"discard this firmware" to the firmware fs.

Also this function is not really necessary, if we set the
filesize of the firmware (truncate()) in firmware fs after
fw_begin_firmware_store() and let the VFS do its magic.

fw_end_firmware_store() will be called, after user space closed
the file descriptor (Note: This will handle SIGKILL also). It
must decide, whether the downloaded firmware is valid and will
be stored and can be used or will be discarded. It gets passed
the context setup by fw_begin_firmware_store() and will free
it's resources, if not needed anymore.

After fw_end_firmware_store(), the firmware can be downloaded to
the device (not before!).

This is much simpler, then it sounds. The only problems are:
1. getting the size of the firmware to be downloaded
a) firmware has always the same size, so this is a constant
b) firmware has size encoded -> use this
c) firmware size is file size -> need to wrap this to be like 1.b)

2. decide, whether the firmware is valid
a) checksum
b) versions
c) none -> trust or wrap to match 2.a) and/or 2.b)

What do you think?

Defining the prototypes and finding the places to hook into is
left as an exercise to the reader ;-)

The current idea (special file sytem) is great, but the interface
to the driver is not really perfect.


Ingo Oeser
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