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authorPavel Begunkov <asml.silence@gmail.com>2021-09-08 22:10:38 +0300
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2021-09-14 11:46:19 +0300
commite5f71d60ff167d0caa491659d65551a55ea6b406 (patch)
tree3a6f7e0b1524aa1e77b4134b12104472a12aa4f1 /drivers/char/mem.c
parent6880fa6c56601bb8ed59df6c30fd390cc5f6dd8f (diff)
downloadlinux-e5f71d60ff167d0caa491659d65551a55ea6b406.tar.xz
/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>
Diffstat (limited to 'drivers/char/mem.c')
-rw-r--r--drivers/char/mem.c8
1 files changed, 6 insertions, 2 deletions
diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index 1c596b5cdb27..cc296f0823bd 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -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 },