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xen-blkback: Apply 'feature_persistent' parameter when connect 

In some use cases[1], the backend is created while the frontend doesn't
support the persistent grants feature, but later the frontend can be
changed to support the feature and reconnect.  In the past, 'blkback'
enabled the persistent grants feature since it unconditionally checked
if frontend supports the persistent grants feature for every connect
('connect_ring()') and decided whether it should use persistent grans or
not.

However, commit aac8a70db2 ("xen-blkback: add a parameter for
disabling of persistent grants") has mistakenly changed the behavior.
It made the frontend feature support check to not be repeated once it
shown the 'feature_persistent' as 'false', or the frontend doesn't
support persistent grants.

This commit changes the behavior of the parameter to make effect for
every connect, so that the previous workflow can work again as expected.

[1] https://lore.kernel.org/xen-devel/CAJwUmVB6H3iTs-C+U=v-pwJB7-_ZRHPxHzKRJZ22xEPW7z8a=g@mail.gmail.com/

Reported-by: Andrii Chepurnyi <andrii.chepurnyi82@gmail.com>
Fixes: aac8a70db2 ("xen-blkback: add a parameter for disabling of persistent grants")
Cc: <stable@vger.kernel.org> # 5.10.x
Signed-off-by: Maximilian Heyne <mheyne@amazon.de>
Signed-off-by: SeongJae Park <sj@kernel.org>
Reviewed-by: Maximilian Heyne <mheyne@amazon.de>
Reviewed-by: Juergen Gross <jgross@suse.com>
Link: https://lore.kernel.org/r/20220715225108.193398-3-sj@kernel.org
Signed-off-by: Juergen Gross <jgross@suse.com>
This commit is contained in:
Maximilian Heyne 2022-07-15 22:51:07 +00:00 committed by Juergen Gross
parent fc9be616bb
commit e94c6101e1
2 changed files with 4 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
Documentation/ABI/testing/sysfs-driver-xen-blkback
View File

@ -42,5 +42,5 @@ KernelVersion: 5.10
Contact: Maximilian Heyne <mheyne@amazon.de>
Description:
Whether to enable the persistent grants feature or not. Note
that this option only takes effect on newly created backends.
that this option only takes effect on newly connected backends.
The default is Y (enable).

9
drivers/block/xen-blkback/xenbus.c
View File

@ -186,8 +186,6 @@ static struct xen_blkif *xen_blkif_alloc(domid_t domid)
__module_get(THIS_MODULE);
INIT_WORK(&blkif->free_work, xen_blkif_deferred_free);
blkif->vbd.feature_gnt_persistent = feature_persistent;
return blkif;
}
@ -1086,10 +1084,9 @@ static int connect_ring(struct backend_info *be)
xenbus_dev_fatal(dev, err, "unknown fe protocol %s", protocol);
return -ENOSYS;
}
if (blkif->vbd.feature_gnt_persistent)
blkif->vbd.feature_gnt_persistent =
xenbus_read_unsigned(dev->otherend,
"feature-persistent", 0);
blkif->vbd.feature_gnt_persistent = feature_persistent &&
xenbus_read_unsigned(dev->otherend, "feature-persistent", 0);
blkif->vbd.overflow_max_grants = 0;