[PATCH v2] io_uring: fix short read slow path

[Dominique Martinet]

sqeq.off here is the offset to read within the disk image, so obviously
not 'nread' (the amount we just read), but as the author meant to write
its current value incremented by the amount we just read.

Normally recent versions of linux will not issue short reads,
but it can happen so we should fix this.

This lead to weird image corruptions when short read happened

Fixes: 6663a0a33764 ("block/io_uring: implements interfaces for io_uring")
Link: https://lkml.kernel.org/r/YrrFGO4A1jS0GI0G@atmark-techno.com
Signed-off-by: Dominique Martinet <dominique.martinet@atmark-techno.com>
---
v1 -> v2: also updated total_read to use += as suggested by Kevin,
thank you!

I've tested this quickly by making short reads "recursives", e.g. added
the following to luring_resubmit_short_read() after setting 'remaining':
    if (remaining > 4096) remaining -= 4096;

so when we ask for more we issue an extra short reads, making sure we go
through the two short reads path.
(Unfortunately I wasn't quite sure what to fiddle with to issue short
reads in the first place, I tried cutting one of the iovs short in
luring_do_submit() but I must not have been doing it properly as I ended
up with 0 return values which are handled by filling in with 0 (reads
after eof) and that didn't work well)

Anyway, this looks OK to me now.

Thanks,
Dominique

 block/io_uring.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/block/io_uring.c b/block/io_uring.c
index d48e472e74cb..b238661740f5 100644
--- a/block/io_uring.c
+++ b/block/io_uring.c
@@ -89,7 +89,7 @@ static void luring_resubmit_short_read(LuringState *s, 
LuringAIOCB *luringcb,
     trace_luring_resubmit_short_read(s, luringcb, nread);
 
     /* Update read position */
-    luringcb->total_read = nread;
+    luringcb->total_read += nread;
     remaining = luringcb->qiov->size - luringcb->total_read;
 
     /* Shorten qiov */
@@ -103,7 +103,7 @@ static void luring_resubmit_short_read(LuringState *s, 
LuringAIOCB *luringcb,
                       remaining);
 
     /* Update sqe */
-    luringcb->sqeq.off = nread;
+    luringcb->sqeq.off += nread;
     luringcb->sqeq.addr = (__u64)(uintptr_t)luringcb->resubmit_qiov.iov;
     luringcb->sqeq.len = luringcb->resubmit_qiov.niov;
 
-- 
2.35.1