block: add block driver read only whitelist

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 a readonly whitelist option, and for
backward compatibility, the old configure option --block-drv-whitelist
is now an alias to rw whitelist.

Drivers in readonly list is only permitted to open file readonly, and
returns -ENOTSUP for RW opening.

E.g. To include vmdk readonly, and others read+write:
    ./configure --target-list=x86_64-softmmu \
                --block-drv-rw-whitelist=qcow2,raw,file,qed \
                --block-drv-ro-whitelist=vmdk

Signed-off-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

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[] = {
+    static const char *whitelist_rw[] = {
-        CONFIG_BDRV_WHITELIST
+        CONFIG_BDRV_RW_WHITELIST
+    };
+    static const char *whitelist_ro[] = {
+        CONFIG_BDRV_RO_WHITELIST
     };
     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);

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;

configure

@@ -123,7 +123,8 @@ interp_prefix="/usr/gnemul/qemu-%M"
 static="no"
 cross_prefix=""
 audio_drv_list=""
-block_drv_whitelist=""
+block_drv_rw_whitelist=""
+block_drv_ro_whitelist=""
 host_cc="cc"
 libs_softmmu=""
 libs_tools=""
@@ -708,7 +709,9 @@ for opt do
   ;;
   --audio-drv-list=*) audio_drv_list="$optarg"
   ;;
-  --block-drv-whitelist=*) block_drv_whitelist=`echo "$optarg" | sed -e 's/,/ /g'`
+  --block-drv-rw-whitelist=*|--block-drv-whitelist=*) block_drv_rw_whitelist=`echo "$optarg" | sed -e 's/,/ /g'`
+  ;;
+  --block-drv-ro-whitelist=*) block_drv_ro_whitelist=`echo "$optarg" | sed -e 's/,/ /g'`
   ;;
   --enable-debug-tcg) debug_tcg="yes"
   ;;
@@ -1049,7 +1052,12 @@ echo "  --disable-cocoa          disable Cocoa (Mac OS X only)"
 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 "  --block-drv-whitelist=L  Same as --block-drv-rw-whitelist=L"
+echo "  --block-drv-rw-whitelist=L"
+echo "                           set block driver read-write whitelist"
+echo "                           (affects only QEMU, not qemu-img)"
+echo "  --block-drv-ro-whitelist=L"
+echo "                           set block driver read-only whitelist"
 echo "                           (affects only QEMU, not qemu-img)"
 echo "  --enable-mixemu          enable mixer emulation"
 echo "  --disable-xen            disable xen backend driver support"
@@ -3481,7 +3489,8 @@ echo "curses support    $curses"
 echo "curl support      $curl"
 echo "mingw32 support   $mingw32"
 echo "Audio drivers     $audio_drv_list"
-echo "Block whitelist   $block_drv_whitelist"
+echo "Block whitelist (rw) $block_drv_rw_whitelist"
+echo "Block whitelist (ro) $block_drv_ro_whitelist"
 echo "Mixer emulation   $mixemu"
 echo "VirtFS support    $virtfs"
 echo "VNC support       $vnc"
@@ -3662,7 +3671,8 @@ fi
 if test "$audio_win_int" = "yes" ; then
   echo "CONFIG_AUDIO_WIN_INT=y" >> $config_host_mak
 fi
-echo "CONFIG_BDRV_WHITELIST=$block_drv_whitelist" >> $config_host_mak
+echo "CONFIG_BDRV_RW_WHITELIST=$block_drv_rw_whitelist" >> $config_host_mak
+echo "CONFIG_BDRV_RO_WHITELIST=$block_drv_ro_whitelist" >> $config_host_mak
 if test "$mixemu" = "yes" ; then
   echo "CONFIG_MIXEMU=y" >> $config_host_mak
 fi

hw/block/xen_disk.c

@@ -780,11 +780,13 @@ static int blk_connect(struct XenDevice *xendev)
 {
     struct XenBlkDev *blkdev = container_of(xendev, struct XenBlkDev, xendev);
     int pers, index, qflags;
+    bool readonly = true;
 
     /* read-only ? */
     qflags = BDRV_O_CACHE_WB | BDRV_O_NATIVE_AIO;
     if (strcmp(blkdev->mode, "w") == 0) {
         qflags |= BDRV_O_RDWR;
+        readonly = false;
     }
 
     /* init qemu block driver */
@@ -795,8 +797,10 @@ static int blk_connect(struct XenDevice *xendev)
         xen_be_printf(&blkdev->xendev, 2, "create new bdrv (xenbus setup)\n");
         blkdev->bs = bdrv_new(blkdev->dev);
         if (blkdev->bs) {
-            if (bdrv_open(blkdev->bs, blkdev->filename, NULL, qflags,
+            BlockDriver *drv = bdrv_find_whitelisted_format(blkdev->fileproto,
-                        bdrv_find_whitelisted_format(blkdev->fileproto)) != 0) {
+                                                           readonly);
+            if (bdrv_open(blkdev->bs,
+                          blkdev->filename, NULL, qflags, drv) != 0) {
                 bdrv_delete(blkdev->bs);
                 blkdev->bs = NULL;
             }

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);

scripts/create_config

@@ -34,8 +34,15 @@ case $line in
     done
     echo ""
     ;;
- CONFIG_BDRV_WHITELIST=*)
+ CONFIG_BDRV_RW_WHITELIST=*)
-    echo "#define CONFIG_BDRV_WHITELIST \\"
+    echo "#define CONFIG_BDRV_RW_WHITELIST\\"
+    for drv in ${line#*=}; do
+      echo "    \"${drv}\",\\"
+    done
+    echo "    NULL"
+    ;;
+ CONFIG_BDRV_RO_WHITELIST=*)
+    echo "#define CONFIG_BDRV_RO_WHITELIST\\"
     for drv in ${line#*=}; do
       echo "    \"${drv}\",\\"
     done