[Xen-devel] [PATCH v2 1/3] xen-blkfront: introduce blkfront_gather_backend_features()

[Bob Liu <bob.liu@xxxxxxxxxx>]

There is a bug when migrate from !feature-persistent host to feature-persistent
host, because domU still thinks new host/backend doesn't support persistent.
Dmesg like:
backed has not unmapped grant: 839
backed has not unmapped grant: 773
backed has not unmapped grant: 773
backed has not unmapped grant: 773
backed has not unmapped grant: 839

The fix is to recheck feature-persistent of new backend in blkif_recover().
See: https://lkml.org/lkml/2015/5/25/469

As Roger suggested, we can split the part of blkfront_connect that checks for
optional features, like persistent grants, indirect descriptors and
flush/barrier features to a separate function and call it from both
blkfront_connect and blkif_recover

Signed-off-by: Bob Liu <bob.liu@xxxxxxxxxx>
---
Changes in v2:
 * Also put blkfront_setup_indirect() inside
---
 drivers/block/xen-blkfront.c |  122 +++++++++++++++++++++++-------------------
 1 file changed, 68 insertions(+), 54 deletions(-)

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 5b45ee5..3b193cf 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -181,6 +181,7 @@ static DEFINE_SPINLOCK(minor_lock);
        ((_segs + SEGS_PER_INDIRECT_FRAME - 1)/SEGS_PER_INDIRECT_FRAME)
 
 static int blkfront_setup_indirect(struct blkfront_info *info);
+static int blkfront_gather_backend_features(struct blkfront_info *info);
 
 static int get_id_from_freelist(struct blkfront_info *info)
 {
@@ -1514,7 +1515,7 @@ static int blkif_recover(struct blkfront_info *info)
        info->shadow_free = info->ring.req_prod_pvt;
        info->shadow[BLK_RING_SIZE(info)-1].req.u.rw.id = 0x0fffffff;
 
-       rc = blkfront_setup_indirect(info);
+       rc = blkfront_gather_backend_features(info);
        if (rc) {
                kfree(copy);
                return rc;
@@ -1694,20 +1695,13 @@ static void blkfront_setup_discard(struct blkfront_info 
*info)
 
 static int blkfront_setup_indirect(struct blkfront_info *info)
 {
-       unsigned int indirect_segments, segs;
+       unsigned int segs;
        int err, i;
 
-       err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
-                           "feature-max-indirect-segments", "%u", 
&indirect_segments,
-                           NULL);
-       if (err) {
-               info->max_indirect_segments = 0;
+       if (info->max_indirect_segments == 0)
                segs = BLKIF_MAX_SEGMENTS_PER_REQUEST;
-       } else {
-               info->max_indirect_segments = min(indirect_segments,
-                                                 xen_blkif_max_segments);
+       else
                segs = info->max_indirect_segments;
-       }
 
        err = fill_grant_buffer(info, (segs + INDIRECT_GREFS(segs)) * 
BLK_RING_SIZE(info));
        if (err)
@@ -1771,6 +1765,68 @@ out_of_memory:
 }
 
 /*
+ * Gather all backend feature-*
+ */
+static int blkfront_gather_backend_features(struct blkfront_info *info)
+{
+       int err;
+       int barrier, flush, discard, persistent;
+       unsigned int indirect_segments;
+
+       info->feature_flush = 0;
+
+       err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
+                       "feature-barrier", "%d", &barrier,
+                       NULL);
+
+       /*
+        * If there's no "feature-barrier" defined, then it means
+        * we're dealing with a very old backend which writes
+        * synchronously; nothing to do.
+        *
+        * If there are barriers, then we use flush.
+        */
+       if (!err && barrier)
+               info->feature_flush = REQ_FLUSH | REQ_FUA;
+       /*
+        * And if there is "feature-flush-cache" use that above
+        * barriers.
+        */
+       err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
+                       "feature-flush-cache", "%d", &flush,
+                       NULL);
+
+       if (!err && flush)
+               info->feature_flush = REQ_FLUSH;
+
+       err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
+                       "feature-discard", "%d", &discard,
+                       NULL);
+
+       if (!err && discard)
+               blkfront_setup_discard(info);
+
+       err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
+                       "feature-persistent", "%u", &persistent,
+                       NULL);
+       if (err)
+               info->feature_persistent = 0;
+       else
+               info->feature_persistent = persistent;
+
+       err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
+                           "feature-max-indirect-segments", "%u", 
&indirect_segments,
+                           NULL);
+       if (err)
+               info->max_indirect_segments = 0;
+       else
+               info->max_indirect_segments = min(indirect_segments,
+                                                 xen_blkif_max_segments);
+
+       return blkfront_setup_indirect(info);
+}
+
+/*
  * Invoked when the backend is finally 'ready' (and has told produced
  * the details about the physical device - #sectors, size, etc).
  */
@@ -1781,7 +1837,6 @@ static void blkfront_connect(struct blkfront_info *info)
        unsigned int physical_sector_size;
        unsigned int binfo;
        int err;
-       int barrier, flush, discard, persistent;
 
        switch (info->connected) {
        case BLKIF_STATE_CONNECTED:
@@ -1838,48 +1893,7 @@ static void blkfront_connect(struct blkfront_info *info)
        if (err != 1)
                physical_sector_size = sector_size;
 
-       info->feature_flush = 0;
-
-       err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
-                           "feature-barrier", "%d", &barrier,
-                           NULL);
-
-       /*
-        * If there's no "feature-barrier" defined, then it means
-        * we're dealing with a very old backend which writes
-        * synchronously; nothing to do.
-        *
-        * If there are barriers, then we use flush.
-        */
-       if (!err && barrier)
-               info->feature_flush = REQ_FLUSH | REQ_FUA;
-       /*
-        * And if there is "feature-flush-cache" use that above
-        * barriers.
-        */
-       err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
-                           "feature-flush-cache", "%d", &flush,
-                           NULL);
-
-       if (!err && flush)
-               info->feature_flush = REQ_FLUSH;
-
-       err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
-                           "feature-discard", "%d", &discard,
-                           NULL);
-
-       if (!err && discard)
-               blkfront_setup_discard(info);
-
-       err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
-                           "feature-persistent", "%u", &persistent,
-                           NULL);
-       if (err)
-               info->feature_persistent = 0;
-       else
-               info->feature_persistent = persistent;
-
-       err = blkfront_setup_indirect(info);
+       err = blkfront_gather_backend_features(info);
        if (err) {
                xenbus_dev_fatal(info->xbdev, err, "setup_indirect at %s",
                                 info->xbdev->otherend);
-- 
1.7.10.4


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