watch_queue: Drop references to /dev/watch_queue

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

Fixes: f7e47677e39a ("watch_que

watch_queue: Drop references to /dev/watch_queue

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 <[email protected]>
Signed-off-by: David Howells <[email protected]>
Acked-by: Jarkko Sakkinen <[email protected]>
Reviewed-by: Ben Boeckel <[email protected]>

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pipe: Add notification lossage handling

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 th

pipe: Add notification lossage handling

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 <[email protected]>

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

Allow a buffer to be marked such that read() must return the entire buffer
in one go or return ENOBUFS. Multiple buffers can b

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

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 <[email protected]>

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Add sample notification program

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

Add sample notification program

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 <[email protected]>

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