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.
Signed-off-by: Pavel Begunkov <asml.silence@xxxxxxxxx>
---
v2:
Don't stop IOCB_NOWAIT read after first page (Jens)
Adjust commit message (following Greg's reply)
iterate nowait until exhausting
drivers/char/mem.c | 8 ++++++--
1 file 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 },
--
2.33.0
