linux-toradex.git/samples/watch_queue/watch_test.c, branch v5.12-rc5

watch_queue: Drop references to /dev/watch_queue

2021-01-21T16:16:08+00:00

The merged API doesn't use a watch_queue device, but instead relies on
pipes, so let the documentation reflect that.

Fixes: f7e47677e39a ("watch_queue: Add a key/keyring notification facility")
Signed-off-by: Gabriel Krisman Bertazi 
Signed-off-by: David Howells 
Acked-by: Jarkko Sakkinen 
Reviewed-by: Ben Boeckel

pipe: Add notification lossage handling

2020-05-19T14:40:28+00:00

Add handling for loss of notifications by having read() insert a
loss-notification message after it has read the pipe buffer that was last
in the ring when the loss occurred.

Lossage can come about either by running out of notification descriptors or
by running out of space in the pipe ring.

Signed-off-by: David Howells

pipe: Allow buffers to be marked read-whole-or-error for notifications

2020-05-19T14:38:18+00:00

Allow a buffer to be marked such that read() must return the entire buffer
in one go or return ENOBUFS.  Multiple buffers can be amalgamated into a
single read, but a short read will occur if the next "whole" buffer won't
fit.

This is useful for watch queue notifications to make sure we don't split a
notification across multiple reads, especially given that we need to
fabricate an overrun record under some circumstances - and that isn't in
the buffers.

Signed-off-by: David Howells

Add sample notification program

2020-05-19T14:38:07+00:00

The sample program is run like:

	./samples/watch_queue/watch_test

and watches "/" for mount changes and the current session keyring for key
changes:

	# keyctl add user a a @s
	1035096409
	# keyctl unlink 1035096409 @s

producing:

	# ./watch_test
	read() = 16
	NOTIFY[000]: ty=000001 sy=02 i=00000110
	KEY 2ffc2e5d change=2[linked] aux=1035096409
	read() = 16
	NOTIFY[000]: ty=000001 sy=02 i=00000110
	KEY 2ffc2e5d change=3[unlinked] aux=1035096409

Other events may be produced, such as with a failing disk:

	read() = 22
	NOTIFY[000]: ty=000003 sy=02 i=00000416
	USB 3-7.7 dev-reset e=0 r=0
	read() = 24
	NOTIFY[000]: ty=000002 sy=06 i=00000418
	BLOCK 00800050 e=6[critical medium] s=64000ef8

This corresponds to:

	blk_update_request: critical medium error, dev sdf, sector 1677725432 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0

in dmesg.

Signed-off-by: David Howells