[Qemu-devel] [PATCH] block: add read only to whitelist

[Fam Zheng <famz@redhat.com>]

We may want to include a driver in the whitelist for read only tasks
such as diagnosing or exporting guest data (with libguestfs as a good
example). This patch introduces the magic prefix ^ to include a driver
to the whitelist, but only enables qemu to open specific image
format readonly, and returns -ENOTSUP for RW opening.

Example: To include vmdk readonly, and others read+write:
    ./configure --block-drv-whitelist=qcow2,raw,file,qed,^vmdk

Signed-off-by: Fam Zheng <famz@redhat.com>
---
 block.c               | 43 +++++++++++++++++++++++++++----------------
 blockdev.c            |  4 ++--
 configure             |  2 ++
 include/block/block.h |  3 ++-
 scripts/create_config |  9 ++++++++-
 5 files changed, 41 insertions(+), 20 deletions(-)

diff --git a/block.c b/block.c
index 3f87489..e6a7270 100644
--- a/block.c
+++ b/block.c
@@ -328,28 +328,40 @@ BlockDriver *bdrv_find_format(const char *format_name)
     return NULL;
 }
 
-static int bdrv_is_whitelisted(BlockDriver *drv)
+static int bdrv_is_whitelisted(BlockDriver *drv, bool read_only)
 {
-    static const char *whitelist[] = {
-        CONFIG_BDRV_WHITELIST
+    static const char *whitelist_rw[] = {
+        CONFIG_BDRV_WHITELIST_RW
+    };
+    static const char *whitelist_ro[] = {
+        CONFIG_BDRV_WHITELIST_RO
     };
     const char **p;
 
-    if (!whitelist[0])
+    if (!whitelist_rw[0] && !whitelist_ro[0]) {
         return 1;               /* no whitelist, anything goes */
+    }
 
-    for (p = whitelist; *p; p++) {
+    for (p = whitelist_rw; *p; p++) {
         if (!strcmp(drv->format_name, *p)) {
             return 1;
         }
     }
+    if (read_only) {
+        for (p = whitelist_ro; *p; p++) {
+            if (!strcmp(drv->format_name, *p)) {
+                return 1;
+            }
+        }
+    }
     return 0;
 }
 
-BlockDriver *bdrv_find_whitelisted_format(const char *format_name)
+BlockDriver *bdrv_find_whitelisted_format(const char *format_name,
+                                          bool read_only)
 {
     BlockDriver *drv = bdrv_find_format(format_name);
-    return drv && bdrv_is_whitelisted(drv) ? drv : NULL;
+    return drv && bdrv_is_whitelisted(drv, read_only) ? drv : NULL;
 }
 
 typedef struct CreateCo {
@@ -684,10 +696,6 @@ static int bdrv_open_common(BlockDriverState *bs, BlockDriverState *file,
 
     trace_bdrv_open_common(bs, filename ?: "", flags, drv->format_name);
 
-    if (use_bdrv_whitelist && !bdrv_is_whitelisted(drv)) {
-        return -ENOTSUP;
-    }
-
     /* bdrv_open() with directly using a protocol as drv. This layer is already
      * opened, so assign it to bs (while file becomes a closed BlockDriverState)
      * and return immediately. */
@@ -698,9 +706,15 @@ static int bdrv_open_common(BlockDriverState *bs, BlockDriverState *file,
 
     bs->open_flags = flags;
     bs->buffer_alignment = 512;
+    open_flags = bdrv_open_flags(bs, flags);
+    bs->read_only = !(open_flags & BDRV_O_RDWR);
+
+    if (use_bdrv_whitelist && !bdrv_is_whitelisted(drv, bs->read_only)) {
+        return -ENOTSUP;
+    }
 
     assert(bs->copy_on_read == 0); /* bdrv_new() and bdrv_close() make it so */
-    if ((flags & BDRV_O_RDWR) && (flags & BDRV_O_COPY_ON_READ)) {
+    if (!bs->read_only && (flags & BDRV_O_COPY_ON_READ)) {
         bdrv_enable_copy_on_read(bs);
     }
 
@@ -714,9 +728,6 @@ static int bdrv_open_common(BlockDriverState *bs, BlockDriverState *file,
     bs->opaque = g_malloc0(drv->instance_size);
 
     bs->enable_write_cache = !!(flags & BDRV_O_CACHE_WB);
-    open_flags = bdrv_open_flags(bs, flags);
-
-    bs->read_only = !(open_flags & BDRV_O_RDWR);
 
     /* Open the image, either directly or using a protocol */
     if (drv->bdrv_file_open) {
@@ -801,7 +812,7 @@ int bdrv_file_open(BlockDriverState **pbs, const char *filename,
     /* Find the right block driver */
     drvname = qdict_get_try_str(options, "driver");
     if (drvname) {
-        drv = bdrv_find_whitelisted_format(drvname);
+        drv = bdrv_find_whitelisted_format(drvname, !(flags & BDRV_O_RDWR));
         qdict_del(options, "driver");
     } else if (filename) {
         drv = bdrv_find_protocol(filename);
diff --git a/blockdev.c b/blockdev.c
index d1ec99a..b9b2d10 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -477,7 +477,7 @@ DriveInfo *drive_init(QemuOpts *all_opts, BlockInterfaceType block_default_type)
             error_printf("\n");
             return NULL;
         }
-        drv = bdrv_find_whitelisted_format(buf);
+        drv = bdrv_find_whitelisted_format(buf, ro);
         if (!drv) {
             error_report("'%s' invalid format", buf);
             return NULL;
@@ -1096,7 +1096,7 @@ void qmp_change_blockdev(const char *device, const char *filename,
     }
 
     if (format) {
-        drv = bdrv_find_whitelisted_format(format);
+        drv = bdrv_find_whitelisted_format(format, bs->read_only);
         if (!drv) {
             error_set(errp, QERR_INVALID_BLOCK_FORMAT, format);
             return;
diff --git a/configure b/configure
index eb74510..87bf54c 100755
--- a/configure
+++ b/configure
@@ -1106,6 +1106,8 @@ echo "  --enable-cocoa           enable Cocoa (default on Mac OS X)"
 echo "  --audio-drv-list=LIST    set audio drivers list:"
 echo "                           Available drivers: $audio_possible_drivers"
 echo "  --block-drv-whitelist=L  set block driver whitelist"
+echo "                           prefix with ^ to include driver readonly"
+echo "                           e.g. --block-drv-whitelist=raw,file,^vmdk"
 echo "                           (affects only QEMU, not qemu-img)"
 echo "  --enable-mixemu          enable mixer emulation"
 echo "  --disable-xen            disable xen backend driver support"
diff --git a/include/block/block.h b/include/block/block.h
index 1251c5c..5604418 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -124,7 +124,8 @@ void bdrv_init(void);
 void bdrv_init_with_whitelist(void);
 BlockDriver *bdrv_find_protocol(const char *filename);
 BlockDriver *bdrv_find_format(const char *format_name);
-BlockDriver *bdrv_find_whitelisted_format(const char *format_name);
+BlockDriver *bdrv_find_whitelisted_format(const char *format_name,
+                                          bool readonly);
 int bdrv_create(BlockDriver *drv, const char* filename,
     QEMUOptionParameter *options);
 int bdrv_create_file(const char* filename, QEMUOptionParameter *options);
diff --git a/scripts/create_config b/scripts/create_config
index c471e8c..2dfda3e 100755
--- a/scripts/create_config
+++ b/scripts/create_config
@@ -35,11 +35,18 @@ case $line in
     echo ""
     ;;
  CONFIG_BDRV_WHITELIST=*)
-    echo "#define CONFIG_BDRV_WHITELIST \\"
+    echo "#define CONFIG_BDRV_WHITELIST_RW \\"
     for drv in ${line#*=}; do
+      [[ "${drv}" = ^* ]] && continue;
       echo "    \"${drv}\",\\"
     done
     echo "    NULL"
+    echo "#define CONFIG_BDRV_WHITELIST_RO \\"
+    for drv in ${line#*=}; do
+      [[ "${drv}" != ^* ]] && continue;
+      echo "    \"${drv#^}\",\\"
+    done
+    echo "    NULL"
     ;;
  CONFIG_*=y) # configuration
     name=${line%=*}
-- 
1.8.2.3