| Message ID | 1464151079-4341-1-git-send-email-eblake@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 25/05/2016 06:37, Eric Blake wrote: > Similar to commit df7b97ff, we are mishandling clients that > give an unaligned NBD_CMD_TRIM request, and potentially > trimming bytes that occur before their request; which in turn > can cause potential unintended data loss (unlikely in > practice, since most clients are sane and issue aligned trim > requests). However, while we fixed read and write by switching > to the byte interfaces of blk_, we don't yet have a byte > interface for discard. On the other hand, trim is advisory, so > rounding the user's request to simply ignore the first and last > unaligned sectors (or the entire request, if it is sub-sector > in length) is just fine. > > CC: qemu-stable@nongnu.org > Signed-off-by: Eric Blake <eblake@redhat.com> > --- > nbd/server.c | 8 ++++++-- > 1 file changed, 6 insertions(+), 2 deletions(-) > > diff --git a/nbd/server.c b/nbd/server.c > index fa862cd..5aed8db 100644 > --- a/nbd/server.c > +++ b/nbd/server.c > @@ -1153,8 +1153,12 @@ static void nbd_trip(void *opaque) > break; > case NBD_CMD_TRIM: > TRACE("Request type is TRIM"); > - ret = blk_co_discard(exp->blk, (request.from + exp->dev_offset) > - / BDRV_SECTOR_SIZE, > + /* Ignore unaligned head or tail, until block layer adds byte > + * interface */ > + request.len -= (request.from + request.len) % BDRV_SECTOR_SIZE; > + ret = blk_co_discard(exp->blk, > + DIV_ROUND_UP(request.from + exp->dev_offset, > + BDRV_SECTOR_SIZE), > request.len / BDRV_SECTOR_SIZE); > if (ret < 0) { > LOG("discard failed"); > Thanks, queued for 2.7. Paolo
On 05/25/2016 02:31 AM, Paolo Bonzini wrote: > > > On 25/05/2016 06:37, Eric Blake wrote: >> Similar to commit df7b97ff, we are mishandling clients that >> give an unaligned NBD_CMD_TRIM request, and potentially >> trimming bytes that occur before their request; which in turn >> can cause potential unintended data loss (unlikely in >> practice, since most clients are sane and issue aligned trim >> requests). However, while we fixed read and write by switching >> to the byte interfaces of blk_, we don't yet have a byte >> interface for discard. On the other hand, trim is advisory, so >> rounding the user's request to simply ignore the first and last >> unaligned sectors (or the entire request, if it is sub-sector >> in length) is just fine. >> >> CC: qemu-stable@nongnu.org >> Signed-off-by: Eric Blake <eblake@redhat.com> >> --- >> nbd/server.c | 8 ++++++-- >> 1 file changed, 6 insertions(+), 2 deletions(-) >> >> diff --git a/nbd/server.c b/nbd/server.c >> index fa862cd..5aed8db 100644 >> --- a/nbd/server.c >> +++ b/nbd/server.c >> @@ -1153,8 +1153,12 @@ static void nbd_trip(void *opaque) >> break; >> case NBD_CMD_TRIM: >> TRACE("Request type is TRIM"); >> - ret = blk_co_discard(exp->blk, (request.from + exp->dev_offset) >> - / BDRV_SECTOR_SIZE, >> + /* Ignore unaligned head or tail, until block layer adds byte >> + * interface */ >> + request.len -= (request.from + request.len) % BDRV_SECTOR_SIZE; Gaaah - this version can underflow request.len. v2 coming up. > Thanks, queued for 2.7. Fortunately, rebasing a staging queue is easier than dealing with an incorrect pull request.
diff --git a/nbd/server.c b/nbd/server.c index fa862cd..5aed8db 100644 --- a/nbd/server.c +++ b/nbd/server.c @@ -1153,8 +1153,12 @@ static void nbd_trip(void *opaque) break; case NBD_CMD_TRIM: TRACE("Request type is TRIM"); - ret = blk_co_discard(exp->blk, (request.from + exp->dev_offset) - / BDRV_SECTOR_SIZE, + /* Ignore unaligned head or tail, until block layer adds byte + * interface */ + request.len -= (request.from + request.len) % BDRV_SECTOR_SIZE; + ret = blk_co_discard(exp->blk, + DIV_ROUND_UP(request.from + exp->dev_offset, + BDRV_SECTOR_SIZE), request.len / BDRV_SECTOR_SIZE); if (ret < 0) { LOG("discard failed");
Similar to commit df7b97ff, we are mishandling clients that give an unaligned NBD_CMD_TRIM request, and potentially trimming bytes that occur before their request; which in turn can cause potential unintended data loss (unlikely in practice, since most clients are sane and issue aligned trim requests). However, while we fixed read and write by switching to the byte interfaces of blk_, we don't yet have a byte interface for discard. On the other hand, trim is advisory, so rounding the user's request to simply ignore the first and last unaligned sectors (or the entire request, if it is sub-sector in length) is just fine. CC: qemu-stable@nongnu.org Signed-off-by: Eric Blake <eblake@redhat.com> --- nbd/server.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)