Am 06.09.2016 um 21:04 hat Eric Blake geschrieben:
When qemu uses iscsi devices in sg mode, iscsilun->block_size
is left at 0. Prior to commits cf081fca and similar, when
block limits were tracked in sectors, this did not matter:
various block limits were just left at 0. But when we started
scaling by block size, this caused SIGFPE.
One possible solution for SG mode is to just blindly skip ALL
of iscsi_refresh_limits(), since we already short circuit so
many other things in sg mode. But this patch takes a slightly
more conservative approach, and merely guarantees that scaling
will succeed (for SG devices, the scaling is done to the block
layer default of 512 bytes, since we don't know of any iscsi
devices with a smaller block size), while still using multiples
of the original size. Resulting limits may still be zero in SG
mode (that is, we only fix block_size used as a denominator, not
all uses).
Reported-by: Holger Schranz <address@hidden>
Signed-off-by: Eric Blake <address@hidden>
CC: address@hidden
---
I would really appreciate Holger testing this patch. We could
also go with the much shorter patch that just does
if (bs->sg) { return; }
at the top of iscsi_refresh_limits(), but I'm not sure if that
would break anything else in the block layer (we had several,
but not all, limits that were provably left alone at 0 for
sg mode).
Hm, originally I thought that we could even just return for bs->sg in
bdrv_refresh_limits() like below because for SG devices the limits
should never be used, but with scsi-block they might actually be.
Paolo, what do you think?
Anyway, let's go with the above patch first, it's a conservative one
that qemu-stable and possibly downstream can safely backport. If we're
going to add anything else, that would be for 2.8 only.
Kevin
diff --git a/block/io.c b/block/io.c
index fdf7080..144ff65 100644
--- a/block/io.c
+++ b/block/io.c
@@ -84,7 +84,7 @@ void bdrv_refresh_limits(BlockDriverState *bs, Error **errp)
memset(&bs->bl, 0, sizeof(bs->bl));
- if (!drv) {
+ if (!drv || bs->sg) {
return;
}