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[Qemu-block] [PATCH v3 06/22] iscsi: Advertise realistic limits to block

From: Eric Blake
Subject: [Qemu-block] [PATCH v3 06/22] iscsi: Advertise realistic limits to block layer
Date: Thu, 23 Jun 2016 16:37:10 -0600

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 <address@hidden>
Reviewed-by: Kevin Wolf <address@hidden>
Reviewed-by: Fam Zheng <address@hidden>
Reviewed-by: Stefan Hajnoczi <address@hidden>

v3: no change
v2: new patch
 block/iscsi.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/block/iscsi.c b/block/iscsi.c
index 7e78ade..4290e41 100644
--- a/block/iscsi.c
+++ b/block/iscsi.c
@@ -1697,7 +1697,9 @@ 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)

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