[Qemu-devel] [for-2.9 4/8] block: Document -drive problematic code and bugs

[Markus Armbruster]

-blockdev and blockdev_add convert their arguments via QObject to
BlockdevOptions for qmp_blockdev_add(), which converts them back to
QObject, then to a flattened QDict.  The QDict's members are typed
according to the QAPI schema.

-drive converts its argument via QemuOpts to a (flat) QDict.  This
QDict's members are all QString.

Thus, the QType of a flat QDict member depends on whether it comes
from -drive or -blockdev/blockdev_add, except when the QAPI type maps
to QString, which is the case for 'str' and enumeration types.

The block layer core extracts generic configuration from the flat
QDict, and the block driver extracts driver-specific configuration.

Both commonly do so by converting (parts of) the flat QDict to
QemuOpts, which turns all values into strings.  Not exactly elegant,
but correct.

However, A few places access the flat QDict directly:

* Most of them access members that are always QString.  Correct.

* bdrv_open_inherit() accesses a boolean, carefully.  Correct.

* nfs_config() uses a QObject input visitor.  Correct only because the
  visited type contains nothing but QStrings.

* nbd_config() and ssh_config() use a QObject input visitor, and the
  visited types contain non-QStrings: InetSocketAddress members
  @numeric, @to, @ipv4, @ipv6.  -drive works as long as you don't try
  to use them (they're all optional).  @to is ignored anyway.

  Reproducer:
  -drive driver=ssh,server.host=h,server.port=22,server.ipv4,path=p
  -drive 
driver=nbd,server.type=inet,server.data.host=h,server.data.port=22,server.data.ipv4
  both fail with "Invalid parameter type for 'data.ipv4', expected: boolean"

Add suitable comments to all these places.  Mark the buggy ones FIXME.

"Fortunately", -drive's driver-specific options are entirely
undocumented.

Signed-off-by: Markus Armbruster <address@hidden>
---
 block.c            | 41 +++++++++++++++++++++++++++++++++++++++--
 block/file-posix.c |  6 ++++++
 block/nbd.c        |  8 ++++++++
 block/nfs.c        |  7 +++++++
 block/rbd.c        |  6 ++++++
 block/ssh.c        |  8 ++++++++
 6 files changed, 74 insertions(+), 2 deletions(-)

diff --git a/block.c b/block.c
index 6e906ec..b3ce23f 100644
--- a/block.c
+++ b/block.c
@@ -1157,6 +1157,12 @@ static int bdrv_open_common(BlockDriverState *bs, 
BlockBackend *file,
     if (file != NULL) {
         filename = blk_bs(file)->filename;
     } else {
+       /*
+        * Caution: direct use of non-string @options members is
+        * problematic.  When they come from -blockdev or blockdev_add,
+        * members are typed according to the QAPI schema, but when
+        * they come from -drive, they're all QString.
+        */
         filename = qdict_get_try_str(options, "filename");
     }
 
@@ -1324,6 +1330,12 @@ static int bdrv_fill_options(QDict **options, const char 
*filename,
     BlockDriver *drv = NULL;
     Error *local_err = NULL;
 
+    /*
+     * Caution: direct use of non-string @options members is
+     * problematic.  When they come from -blockdev or blockdev_add,
+     * members are typed according to the QAPI schema, but when they
+     * come from -drive, they're all QString.
+     */
     drvname = qdict_get_try_str(*options, "driver");
     if (drvname) {
         drv = bdrv_find_format(drvname);
@@ -1358,6 +1370,7 @@ static int bdrv_fill_options(QDict **options, const char 
*filename,
     }
 
     /* Find the right block driver */
+    /* Direct use of @options members is problematic, see note above */
     filename = qdict_get_try_str(*options, "filename");
 
     if (!drvname && protocol) {
@@ -1987,6 +2000,12 @@ int bdrv_open_backing_file(BlockDriverState *bs, QDict 
*parent_options,
     qdict_extract_subqdict(parent_options, &options, bdref_key_dot);
     g_free(bdref_key_dot);
 
+    /*
+     * Caution: direct use of non-string @parent_options members is
+     * problematic.  When they come from -blockdev or blockdev_add,
+     * members are typed according to the QAPI schema, but when they
+     * come from -drive, they're all QString.
+     */
     reference = qdict_get_try_str(parent_options, bdref_key);
     if (reference || qdict_haskey(options, "file.filename")) {
         backing_filename[0] = '\0';
@@ -2059,6 +2078,12 @@ bdrv_open_child_bs(const char *filename, QDict *options, 
const char *bdref_key,
     qdict_extract_subqdict(options, &image_options, bdref_key_dot);
     g_free(bdref_key_dot);
 
+    /*
+     * Caution: direct use of non-string @options members is
+     * problematic.  When they come from -blockdev or blockdev_add,
+     * members are typed according to the QAPI schema, but when they
+     * come from -drive, they're all QString.
+     */
     reference = qdict_get_try_str(options, bdref_key);
     if (!filename && !reference && !qdict_size(image_options)) {
         if (!allow_none) {
@@ -2275,8 +2300,11 @@ static BlockDriverState *bdrv_open_inherit(const char 
*filename,
     }
 
     /* Set the BDRV_O_RDWR and BDRV_O_ALLOW_RDWR flags.
-     * FIXME: we're parsing the QDict to avoid having to create a
-     * QemuOpts just for this, but neither option is optimal. */
+     * Caution: direct use of non-string @options members is
+     * problematic.  When they come from -blockdev or blockdev_add,
+     * members are typed according to the QAPI schema, but when they
+     * come from -drive, they're all QString.
+     */
     if (g_strcmp0(qdict_get_try_str(options, BDRV_OPT_READ_ONLY), "on") &&
         !qdict_get_try_bool(options, BDRV_OPT_READ_ONLY, false)) {
         flags |= (BDRV_O_RDWR | BDRV_O_ALLOW_RDWR);
@@ -2298,6 +2326,7 @@ static BlockDriverState *bdrv_open_inherit(const char 
*filename,
     options = qdict_clone_shallow(options);
 
     /* Find the right image format driver */
+    /* Direct use of @options members is problematic, see note above */
     drvname = qdict_get_try_str(options, "driver");
     if (drvname) {
         drv = bdrv_find_format(drvname);
@@ -2309,6 +2338,7 @@ static BlockDriverState *bdrv_open_inherit(const char 
*filename,
 
     assert(drvname || !(flags & BDRV_O_PROTOCOL));
 
+    /* Direct use of @options members is problematic, see note above */
     backing = qdict_get_try_str(options, "backing");
     if (backing && *backing == '\0') {
         flags |= BDRV_O_NO_BACKING;
@@ -2787,6 +2817,13 @@ int bdrv_reopen_prepare(BDRVReopenState *reopen_state, 
BlockReopenQueue *queue,
         do {
             QString *new_obj = qobject_to_qstring(entry->value);
             const char *new = qstring_get_str(new_obj);
+           /*
+            * Caution: direct use of non-string bs->options members is
+            * problematic.  When they come from -blockdev or
+            * blockdev_add, members are typed according to the QAPI
+            * schema, but when they come from -drive, they're all
+            * QString.
+            */
             const char *old = qdict_get_try_str(reopen_state->bs->options,
                                                 entry->key);
 
diff --git a/block/file-posix.c b/block/file-posix.c
index 0841a08..738541e 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -2193,6 +2193,12 @@ static int hdev_open(BlockDriverState *bs, QDict 
*options, int flags,
     int ret;
 
 #if defined(__APPLE__) && defined(__MACH__)
+    /*
+     * Caution: direct use of non-string @options members is
+     * problematic.  When they come from -blockdev or blockdev_add,
+     * members are typed according to the QAPI schema, but when they
+     * come from -drive, they're all QString.
+     */
     const char *filename = qdict_get_str(options, "filename");
     char bsd_path[MAXPATHLEN] = "";
     bool error_occurred = false;
diff --git a/block/nbd.c b/block/nbd.c
index 36ea617..11e3ba7 100644
--- a/block/nbd.c
+++ b/block/nbd.c
@@ -278,6 +278,14 @@ static SocketAddress *nbd_config(BDRVNBDState *s, QDict 
*options, Error **errp)
         goto done;
     }
 
+    /*
+     * FIXME .numeric, .to, .ipv4 or .ipv6 don't work with -drive
+     * server.type=inet.  .to doesn't matter, it's ignored anyway.
+     * That's because when @options come from -blockdev or
+     * blockdev_add, members are typed according to the QAPI schema,
+     * but when they come from -drive, they're all QString.  The
+     * visitor expects the former.
+     */
     iv = qobject_input_visitor_new(crumpled_addr);
     visit_type_SocketAddress(iv, NULL, &saddr, &local_err);
     if (local_err) {
diff --git a/block/nfs.c b/block/nfs.c
index 3f43f6e..42407de 100644
--- a/block/nfs.c
+++ b/block/nfs.c
@@ -474,6 +474,13 @@ static NFSServer *nfs_config(QDict *options, Error **errp)
         goto out;
     }
 
+    /*
+     * Caution: this works only because all scalar members of
+     * NFSServer are QString in @crumpled_addr.  The visitor expects
+     * @crumpled_addr to be typed according to the QAPI scherma.  It
+     * is when @options come from -blockdev or blockdev_add.  But when
+     * they come from -drive, they're all QString.
+     */
     iv = qobject_input_visitor_new(crumpled_addr);
     visit_type_NFSServer(iv, NULL, &server, &local_error);
     if (local_error) {
diff --git a/block/rbd.c b/block/rbd.c
index 498322b..b9a9526 100644
--- a/block/rbd.c
+++ b/block/rbd.c
@@ -384,6 +384,12 @@ static int qemu_rbd_create(const char *filename, QemuOpts 
*opts, Error **errp)
         goto exit;
     }
 
+    /*
+     * Caution: direct use of non-string @options members is
+     * problematic.  When they come from -blockdev or blockdev_add,
+     * members are typed according to the QAPI schema, but when they
+     * come from -drive, they're all QString.
+     */
     pool       = qdict_get_try_str(options, "pool");
     conf       = qdict_get_try_str(options, "conf");
     clientname = qdict_get_try_str(options, "user");
diff --git a/block/ssh.c b/block/ssh.c
index 278e66f..471ba8a 100644
--- a/block/ssh.c
+++ b/block/ssh.c
@@ -601,6 +601,14 @@ static InetSocketAddress *ssh_config(QDict *options, Error 
**errp)
         goto out;
     }
 
+    /*
+     * FIXME .numeric, .to, .ipv4 or .ipv6 don't work with -drive.
+     * .to doesn't matter, it's ignored anyway.
+     * That's because when @options come from -blockdev or
+     * blockdev_add, members are typed according to the QAPI schema,
+     * but when they come from -drive, they're all QString.  The
+     * visitor expects the former.
+     */
     iv = qobject_input_visitor_new(crumpled_addr);
     visit_type_InetSocketAddress(iv, NULL, &inet, &local_error);
     if (local_error) {
-- 
2.7.4