[qemu-xen stable-4.13] block/create: Do not abort if a block driver is not available

[patchbot@xxxxxxx]

commit 088f1e8fd9e790bc5766bd43af134230abcff6dd
Author:     Philippe Mathieu-Daudé <philmd@xxxxxxxxxx>
AuthorDate: Thu Sep 12 00:08:49 2019 +0200
Commit:     Michael Roth <mdroth@xxxxxxxxxxxxxxxxxx>
CommitDate: Tue Nov 12 16:31:38 2019 -0600

    block/create: Do not abort if a block driver is not available
    
    The 'blockdev-create' QMP command was introduced as experimental
    feature in commit b0292b851b8, using the assert() debug call.
    It got promoted to 'stable' command in 3fb588a0f2c, but the
    assert call was not removed.
    
    Some block drivers are optional, and bdrv_find_format() might
    return a NULL value, triggering the assertion.
    
    Stable code is not expected to abort, so return an error instead.
    
    This is easily reproducible when libnfs is not installed:
    
      ./configure
      [...]
      module support    no
      Block whitelist (rw)
      Block whitelist (ro)
      libiscsi support  yes
      libnfs support    no
      [...]
    
    Start QEMU:
    
      $ qemu-system-x86_64 -S -qmp unix:/tmp/qemu.qmp,server,nowait
    
    Send the 'blockdev-create' with the 'nfs' driver:
    
      $ ( cat << 'EOF'
      {'execute': 'qmp_capabilities'}
      {'execute': 'blockdev-create', 'arguments': {'job-id': 'x', 'options': 
{'size': 0, 'driver': 'nfs', 'location': {'path': '/', 'server': {'host': 
'::1', 'type': 'inet'}}}}, 'id': 'x'}
      EOF
      ) | socat STDIO UNIX:/tmp/qemu.qmp
      {"QMP": {"version": {"qemu": {"micro": 50, "minor": 1, "major": 4}, 
"package": "v4.1.0-733-g89ea03a7dc"}, "capabilities": ["oob"]}}
      {"return": {}}
    
    QEMU crashes:
    
      $ gdb qemu-system-x86_64 core
      Program received signal SIGSEGV, Segmentation fault.
      (gdb) bt
      #0  0x00007ffff510957f in raise () at /lib64/libc.so.6
      #1  0x00007ffff50f3895 in abort () at /lib64/libc.so.6
      #2  0x00007ffff50f3769 in _nl_load_domain.cold.0 () at /lib64/libc.so.6
      #3  0x00007ffff5101a26 in .annobin_assert.c_end () at /lib64/libc.so.6
      #4  0x0000555555d7e1f1 in qmp_blockdev_create (job_id=0x555556baee40 "x", 
options=0x555557666610, errp=0x7fffffffc770) at block/create.c:69
      #5  0x0000555555c96b52 in qmp_marshal_blockdev_create 
(args=0x7fffdc003830, ret=0x7fffffffc7f8, errp=0x7fffffffc7f0) at 
qapi/qapi-commands-block-core.c:1314
      #6  0x0000555555deb0a0 in do_qmp_dispatch (cmds=0x55555645de70 
<qmp_commands>, request=0x7fffdc005c70, allow_oob=false, errp=0x7fffffffc898) 
at qapi/qmp-dispatch.c:131
      #7  0x0000555555deb2a1 in qmp_dispatch (cmds=0x55555645de70 
<qmp_commands>, request=0x7fffdc005c70, allow_oob=false) at 
qapi/qmp-dispatch.c:174
    
    With this patch applied, QEMU returns a QMP error:
    
      {'execute': 'blockdev-create', 'arguments': {'job-id': 'x', 'options': 
{'size': 0, 'driver': 'nfs', 'location': {'path': '/', 'server': {'host': 
'::1', 'type': 'inet'}}}}, 'id': 'x'}
      {"id": "x", "error": {"class": "GenericError", "desc": "Block driver 
'nfs' not found or not supported"}}
    
    Cc: qemu-stable@xxxxxxxxxx
    Reported-by: Xu Tian <xutian@xxxxxxxxxx>
    Signed-off-by: Philippe Mathieu-Daudé <philmd@xxxxxxxxxx>
    Reviewed-by: Eric Blake <eblake@xxxxxxxxxx>
    Reviewed-by: John Snow <jsnow@xxxxxxxxxx>
    Signed-off-by: Kevin Wolf <kwolf@xxxxxxxxxx>
    (cherry picked from commit d90d5cae2b10efc0e8d0b3cc91ff16201853d3ba)
    Signed-off-by: Michael Roth <mdroth@xxxxxxxxxxxxxxxxxx>
---
 block/create.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/block/create.c b/block/create.c
index 95341219ef..de5e97bb18 100644
--- a/block/create.c
+++ b/block/create.c
@@ -63,9 +63,13 @@ void qmp_blockdev_create(const char *job_id, 
BlockdevCreateOptions *options,
     const char *fmt = BlockdevDriver_str(options->driver);
     BlockDriver *drv = bdrv_find_format(fmt);
 
+    if (!drv) {
+        error_setg(errp, "Block driver '%s' not found or not supported", fmt);
+        return;
+    }
+
     /* If the driver is in the schema, we know that it exists. But it may not
      * be whitelisted. */
-    assert(drv);
     if (bdrv_uses_whitelist() && !bdrv_is_whitelisted(drv, false)) {
         error_setg(errp, "Driver is not whitelisted");
         return;
--
generated by git-patchbot for /home/xen/git/qemu-xen.git#stable-4.13