[Qemu-devel] [PATCH for-2.10 2/9] block: do not set BDS read_only if copy_on_read enabled

[Jeff Cody]

A few block drivers will set the BDS read_only flag from their
.bdrv_open() function.  This means the bs->read_only flag could
be set after we enable copy_on_read, as the BDRV_O_COPY_ON_READ
flag check occurs prior to the call to bdrv->bdrv_open().

This adds an error return to bdrv_set_read_only(), and an error will be
return if we try to set the BDS to read_only while copy_on_read is
enabled.

Signed-off-by: Jeff Cody <address@hidden>
---
 block.c               | 10 +++++++++-
 block/bochs.c         |  5 ++++-
 block/cloop.c         |  5 ++++-
 block/dmg.c           |  6 +++++-
 block/rbd.c           |  6 +++++-
 block/vvfat.c         | 15 ++++++++++++---
 include/block/block.h |  2 +-
 7 files changed, 40 insertions(+), 9 deletions(-)

diff --git a/block.c b/block.c
index 7b4c7ef..f60d5ea 100644
--- a/block.c
+++ b/block.c
@@ -192,9 +192,17 @@ void path_combine(char *dest, int dest_size,
     }
 }
 
-void bdrv_set_read_only(BlockDriverState *bs, bool read_only)
+int bdrv_set_read_only(BlockDriverState *bs, bool read_only, Error **errp)
 {
+    /* Do not set read_only if copy_on_read is enabled */
+    if (bs->copy_on_read && read_only) {
+        error_setg(errp, "Cannot set node '%s' to r/o while COW enabled",
+                   bdrv_get_device_or_node_name(bs));
+        return -EINVAL;
+    }
+
     bs->read_only = read_only;
+    return 0;
 }
 
 void bdrv_get_full_backing_filename_from_filename(const char *backed,
diff --git a/block/bochs.c b/block/bochs.c
index bdc2831..a759b6e 100644
--- a/block/bochs.c
+++ b/block/bochs.c
@@ -110,7 +110,10 @@ static int bochs_open(BlockDriverState *bs, QDict 
*options, int flags,
         return -EINVAL;
     }
 
-    bdrv_set_read_only(bs, true); /* no write support yet */
+    ret = bdrv_set_read_only(bs, true, errp); /* no write support yet */
+    if (ret < 0) {
+        return ret;
+    }
 
     ret = bdrv_pread(bs->file, 0, &bochs, sizeof(bochs));
     if (ret < 0) {
diff --git a/block/cloop.c b/block/cloop.c
index 11f17c8..d6597fc 100644
--- a/block/cloop.c
+++ b/block/cloop.c
@@ -72,7 +72,10 @@ static int cloop_open(BlockDriverState *bs, QDict *options, 
int flags,
         return -EINVAL;
     }
 
-    bdrv_set_read_only(bs, true);
+    ret = bdrv_set_read_only(bs, true, errp);
+    if (ret < 0) {
+        return ret;
+    }
 
     /* read header */
     ret = bdrv_pread(bs->file, 128, &s->block_size, 4);
diff --git a/block/dmg.c b/block/dmg.c
index 27ce4a6..900ae5a 100644
--- a/block/dmg.c
+++ b/block/dmg.c
@@ -419,8 +419,12 @@ static int dmg_open(BlockDriverState *bs, QDict *options, 
int flags,
         return -EINVAL;
     }
 
+    ret = bdrv_set_read_only(bs, true, errp);
+    if (ret < 0) {
+        return ret;
+    }
+
     block_module_load_one("dmg-bz2");
-    bdrv_set_read_only(bs, true);
 
     s->n_chunks = 0;
     s->offsets = s->lengths = s->sectors = s->sectorcounts = NULL;
diff --git a/block/rbd.c b/block/rbd.c
index 6ad2904..328e4a9 100644
--- a/block/rbd.c
+++ b/block/rbd.c
@@ -641,7 +641,11 @@ static int qemu_rbd_open(BlockDriverState *bs, QDict 
*options, int flags,
         goto failed_open;
     }
 
-    bdrv_set_read_only(bs, (s->snap != NULL));
+    r = bdrv_set_read_only(bs, (s->snap != NULL), &local_err);
+    if (r < 0) {
+        error_propagate(errp, local_err);
+        goto failed_open;
+    }
 
     qemu_opts_del(opts);
     return 0;
diff --git a/block/vvfat.c b/block/vvfat.c
index d4ce6d7..34a2854 100644
--- a/block/vvfat.c
+++ b/block/vvfat.c
@@ -1156,8 +1156,6 @@ static int vvfat_open(BlockDriverState *bs, QDict 
*options, int flags,
 
     s->current_cluster=0xffffffff;
 
-    /* read only is the default for safety */
-    bdrv_set_read_only(bs, true);
     s->qcow = NULL;
     s->qcow_filename = NULL;
     s->fat2 = NULL;
@@ -1173,7 +1171,18 @@ static int vvfat_open(BlockDriverState *bs, QDict 
*options, int flags,
         if (ret < 0) {
             goto fail;
         }
-        bdrv_set_read_only(bs, false);
+        ret = bdrv_set_read_only(bs, false, &local_err);
+        if (ret < 0) {
+            error_propagate(errp, local_err);
+            goto fail;
+        }
+    } else  {
+        /* read only is the default for safety */
+        ret = bdrv_set_read_only(bs, true, &local_err);
+        if (ret < 0) {
+            error_propagate(errp, local_err);
+            goto fail;
+        }
     }
 
     bs->total_sectors = cyls * heads * secs;
diff --git a/include/block/block.h b/include/block/block.h
index 06c9032..beb563a 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -426,7 +426,7 @@ int bdrv_is_allocated_above(BlockDriverState *top, 
BlockDriverState *base,
                             int64_t sector_num, int nb_sectors, int *pnum);
 
 bool bdrv_is_read_only(BlockDriverState *bs);
-void bdrv_set_read_only(BlockDriverState *bs, bool read_only);
+int bdrv_set_read_only(BlockDriverState *bs, bool read_only, Error **errp);
 bool bdrv_is_sg(BlockDriverState *bs);
 bool bdrv_is_inserted(BlockDriverState *bs);
 int bdrv_media_changed(BlockDriverState *bs);
-- 
2.9.3