Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on fallback

[Luis R. Rodriguez]

Adding fsdevel folks.

On Tue, Jun 06, 2017 at 03:53:16PM +0100, Alan Cox wrote:
> > "Unix tradition (and thus almost all applications) believe file store
> > writes to
> > be non signal interruptible. It would not be safe or practical to
> > change that
> > guarantee."
> 
> Yep everyone codes
> 
> 	write(disk_file, "foo", 3);
> 
> not while(..) blah around it.

Thanks for the confirmation! That's a simple enough explanation.

> > For these two reasons then it would seem best we do two things
> > actually:
> > 
> > 1) return -EINTR instead of -EAGAIN when we detect
> > swait_event_interruptible_timeout()
> > got interrupted by a signal (it returns -ERESTARTSYS)
> > 2) Do as you note below and add wait_event_killable_timeout()
> 
> Pedantic detail that I don't think affects you
> 
> If you have completed a part of the I/O then you should return the byte
> processed count not EINTR, but -1,EINTR if no progress was made.

You are right with some new exceptions and with regards to the future:

The syfs loading interface for firmware currently goes through the
data file exposed on syfs, the respective write op firmware_data_write()
only checks for signals at the beginning. After that its a full one
swoop try to write if you are following the old tradition and are using
a buffer allocated by the firmware API.

If you are using the relatively new request_firmware_into_buf() added
by Stephen Boyd which lets the driver provide the allocated buffer then
we have a loop in firmware_rw() which should be fixed to:

1) Check for signals
2) Do what you noted above.

Furthermore Yi Li over at Intel is adding some new API calls which would
re-use some of this for FPGA firmwares which are also very large, that
work should consider the above and fix appropriately as well.

  Luis