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/dev/mem: nowait zero/null ops 

Make read_iter_zero() to honor IOCB_NOWAIT, so /dev/zero can be
advertised as FMODE_NOWAIT. It's useful for io_uring, which needs it to
apply certain optimisations when doing I/O against the device.

Set FMODE_NOWAIT for /dev/null as well, it never waits and therefore
trivially meets the criteria.

Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/f11090f97ddc2b2ce49ea1211258658ddfbc5563.1631127867.git.asml.silence@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Pavel Begunkov 2021-09-08 20:10:38 +01:00 committed by Greg Kroah-Hartman
parent 6880fa6c56
commit e5f71d60ff
1 changed files with 6 additions and 2 deletions
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8
drivers/char/mem.c
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@ -495,6 +495,10 @@ static ssize_t read_iter_zero(struct kiocb *iocb, struct iov_iter *iter)
written += n;
if (signal_pending(current))
return written ? written : -ERESTARTSYS;
if (!need_resched())
continue;
if (iocb->ki_flags & IOCB_NOWAIT)
return written ? written : -EAGAIN;
cond_resched();
}
return written;
@ -696,11 +700,11 @@ static const struct memdev {
#ifdef CONFIG_DEVMEM
[DEVMEM_MINOR] = { "mem", 0, &mem_fops, FMODE_UNSIGNED_OFFSET },
#endif
[3] = { "null", 0666, &null_fops, 0 },
[3] = { "null", 0666, &null_fops, FMODE_NOWAIT },
#ifdef CONFIG_DEVPORT
[4] = { "port", 0, &port_fops, 0 },
#endif
[5] = { "zero", 0666, &zero_fops, 0 },
[5] = { "zero", 0666, &zero_fops, FMODE_NOWAIT },
[7] = { "full", 0666, &full_fops, 0 },
[8] = { "random", 0666, &random_fops, 0 },
[9] = { "urandom", 0666, &urandom_fops, 0 },