On 29/1/2018 10:48 PM, Max Reitz wrote:
On 2018-01-18 18:49, Anton Nefedov wrote:
The idea is that ALLOCATE requests may overlap with other requests.
Reuse the existing block layer infrastructure for serialising requests.
Use the following approach:
- mark ALLOCATE serialising, so subsequent requests to the area wait
- ALLOCATE request itself must never wait if another request is in flight
already. Return EAGAIN, let the caller reconsider.
Signed-off-by: Anton Nefedov <anton.nefe...@virtuozzo.com>
Reviewed-by: Eric Blake <ebl...@redhat.com>
---
block/io.c | 27 +++++++++++++++++++--------
1 file changed, 19 insertions(+), 8 deletions(-)
The basic principle looks good to me.
diff --git a/block/io.c b/block/io.c
index cf2f84c..4b0d34f 100644
--- a/block/io.c
+++ b/block/io.c
[...]
@@ -1717,7 +1728,7 @@ int coroutine_fn bdrv_co_pwritev(BdrvChild *child,
struct iovec head_iov;
mark_request_serialising(&req, align);
- wait_serialising_requests(&req);
+ wait_serialising_requests(&req, false);
What if someone calls bdrv_co_pwritev() with BDRV_REQ_ZERO_WRITE |
BDRV_REQ_ALLOCATE?
Either
assert(!(qiov && (flags & BDRV_REQ_ALLOCATE)));
will fail or bdrv_co_do_zero_pwritev() will be used.
.. Then this should do exactly the same as
bdrv_co_do_zero_pwritev(), which it currently does not -- besides this
serialization, this includes returning -ENOTSUP if there is a head or
tail to write.
Another question is if that assertion is ok.
In other words: should (qiov!=NULL && REQ_ALLOCATE) be a valid case?
e.g. with qiov filled with zeroes?
I'd rather document that not supported (and leave the assertion).
Actually, even (qiov!=NULL && REQ_ZERO_WRITE) looks kind of
unsupported/broken? Alignment code in bdrv_co_pwritev() zeroes out the
head and tail by passing the flag down bdrv_aligned_pwritev()
