mirror_zfs/include/os/linux
Rob N b181b2e604
bdev_discard_supported: understand discard_granularity=0
Kernel documentation for the discard_granularity property says:

    A discard_granularity of 0 means that the device does not support
    discard functionality.

Some older kernels had drivers (notably loop, but also some USB-SATA
adapters) that would set the QUEUE_FLAG_DISCARD capability flag, but
have discard_granularity=0. Since 5.10 (torvalds/linux@b35fd7422c) the
discard entry point blkdev_issue_discard() has had a check for this,
which would immediately reject the call with EOPNOTSUPP, and throw a
scary diagnostic message into the log. See #16068.

Since 6.8, the block layer sets a non-zero default for
discard_granularity (torvalds/linux@3c407dc723), and a future kernel
will remove the check entirely[1].

As such, there's no good reason for us to enable discard when
discard_granularity=0. The kernel will never let the request go in
anyway; better that we just disable it so we can report it properly to
the user.

1. https://patchwork.kernel.org/project/linux-block/patch/20240312144826.1045212-2-hch@lst.de/

Sponsored-by: Klara, Inc.
Sponsored-by: Wasabi Technology, Inc.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Rob Norris <rob.norris@klarasystems.com>
Closes #16068
Closes #16082
2024-04-12 09:00:20 -07:00
..
kernel/linux bdev_discard_supported: understand discard_granularity=0 2024-04-12 09:00:20 -07:00
spl dkio: remove kernel dkio.h compatibility header 2024-04-11 17:17:18 -07:00
zfs/sys zio: remove io_cmd and DKIOCFLUSHWRITECACHE 2024-04-11 17:17:11 -07:00
Makefile.am dkio: remove kernel dkio.h compatibility header 2024-04-11 17:17:18 -07:00