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iscsi: Advertise realistic limits to block layer

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The function sector_limits_lun2qemu() returns a value in units of
the block layer's 512-byte sector, and can be as large as
0x40000000, which is much larger than the block layer's inherent
limit of BDRV_REQUEST_MAX_SECTORS.  The block layer already
handles '0' as a synonym to the inherent limit, and it is nicer
to return this value than it is to calculate an arbitrary
maximum, for two reasons: we want to ensure that the block layer
continues to special-case '0' as 'no limit beyond the inherent
limits'; and we want to be able to someday expand the block
layer to allow 64-bit limits, where auditing for uses of
BDRV_REQUEST_MAX_SECTORS will help us make sure we aren't
artificially constraining iscsi to old block layer limits.

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Eric Blake 2016-06-23 16:37:10 -06:00 committed by Kevin Wolf
parent 202204717a
commit f9e95af0a6
1 changed files with 3 additions and 1 deletions
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4
block/iscsi.c
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@ -1698,7 +1698,9 @@ static void iscsi_close(BlockDriverState *bs)
static int sector_limits_lun2qemu(int64_t sector, IscsiLun *iscsilun)
{
return MIN(sector_lun2qemu(sector, iscsilun), INT_MAX / 2 + 1);
int limit = MIN(sector_lun2qemu(sector, iscsilun), INT_MAX / 2 + 1);
return limit < BDRV_REQUEST_MAX_SECTORS ? limit : 0;
}
static void iscsi_refresh_limits(BlockDriverState *bs, Error **errp)