[Qemu-devel][PATCH] Qemu image over raw devices

[Shahar Frank]

Hi,

The following patch enables QEMU to create and use images with any 
format on top of a raw device. Note that -f <format> is not enough for 
bcking files support.

The patch includes the following:

1. The check for block devices is weaken so you can override it by 
specifying a protocol
2. If a protocol exists but not found in the protocols list, the logic 
falls back to image type probing. This means use can write 
"probe:filename" or just ":filename"

Note that if regular file/device path names are used, the previous 
behavior is kept.

lvcreate -L 5G -n base store
dd bs=32k if=win.qcow2 of=/dev/store/base
./qemu-img info :/dev/store/base
lvcreate -L 2G -n l2 store
./qemu-img create -b :/dev/store/base -f qcow2 /dev/store/l2
./x86_64-softmmu/qemu-system-x86_64 -hda :/dev/store/l2 -L pc-bios/
lvcreate -L 2G -n l3 store
./qemu-img create -b :/dev/store/l2 -f qcow2 /dev/store/l3
./x86_64-softmmu/qemu-system-x86_64 -hda :/dev/store/l3 -L pc-bios/

Signed-off-by: Shahar Frank <address@hidden>

diff --git a/block.c b/block.c
index 28d63d7..cbf9968 100644
--- a/block.c
+++ b/block.c
@@ -226,6 +226,17 @@ static int is_windows_drive(const char *filename)
 }
 #endif

+static const char *raw_filename(const char *filename)
+{
+    char *_filename;
+
+    _filename = strchr(filename, ':');
+    if (_filename)
+        return _filename + 1;
+    else
+        return filename;
+}
+
 static BlockDriver *find_protocol(const char *filename)
 {
     BlockDriver *drv1;
@@ -267,25 +278,28 @@ static BlockDriver *find_image_format(const char 
*filename)
        recognized as a host CDROM */
     if (strstart(filename, "/dev/cdrom", NULL))
         return &bdrv_host_device;
+    drv = find_protocol(filename);
+
+    if (drv == &bdrv_raw) {
 #ifdef _WIN32
-    if (is_windows_drive(filename))
-        return &bdrv_host_device;
+               if (is_windows_drive(filename))
+                       return &bdrv_host_device;
 #else
-    {
-        struct stat st;
-        if (stat(filename, &st) >= 0 &&
-            (S_ISCHR(st.st_mode) || S_ISBLK(st.st_mode))) {
-            return &bdrv_host_device;
-        }
-    }
+               {
+                       struct stat st;
+                       if (stat(filename, &st) >= 0 &&
+                               (S_ISCHR(st.st_mode) || S_ISBLK(st.st_mode))) {
+                                       return &bdrv_host_device;
+                               }
+               }
 #endif
+    }

-    drv = find_protocol(filename);
     /* no need to test disk image formats for vvfat */
     if (drv == &bdrv_vvfat)
         return drv;

-    ret = bdrv_file_open(&bs, filename, BDRV_O_RDONLY);
+    ret = bdrv_file_open(&bs, raw_filename(filename), BDRV_O_RDONLY);
     if (ret < 0)
         return NULL;
     ret = bdrv_pread(bs, 0, buf, sizeof(buf));
@@ -335,6 +349,7 @@ int bdrv_open2(BlockDriverState *bs, const char 
*filename, int flags,
     int ret, open_flags;
     char tmp_filename[PATH_MAX];
     char backing_filename[PATH_MAX];
+    char const *_filename;

     bs->read_only = 0;
     bs->is_temporary = 0;
@@ -403,9 +418,12 @@ int bdrv_open2(BlockDriverState *bs, const char 
*filename, int flags,
         open_flags = BDRV_O_RDWR | (flags & BDRV_O_CACHE_MASK);
     else
         open_flags = flags & ~(BDRV_O_FILE | BDRV_O_SNAPSHOT);
-    ret = drv->bdrv_open(bs, filename, open_flags);
+
+    _filename = raw_filename(filename);
+
+    ret = drv->bdrv_open(bs, _filename, open_flags);
     if ((ret == -EACCES || ret == -EPERM) && !(flags & BDRV_O_FILE)) {
-        ret = drv->bdrv_open(bs, filename, open_flags & ~BDRV_O_RDWR);
+        ret = drv->bdrv_open(bs, _filename, open_flags & ~BDRV_O_RDWR);
         bs->read_only = 1;
     }
     if (ret < 0) {
diff --git a/qemu-img.c b/qemu-img.c


diff --git a/block.c b/block.c
index 28d63d7..cbf9968 100644
--- a/block.c
+++ b/block.c
@@ -226,6 +226,17 @@ static int is_windows_drive(const char *filename)
 }
 #endif
 
+static const char *raw_filename(const char *filename)
+{
+    char *_filename;
+
+    _filename = strchr(filename, ':');
+    if (_filename)
+        return _filename + 1;
+    else
+        return filename;
+}
+
 static BlockDriver *find_protocol(const char *filename)
 {
     BlockDriver *drv1;
@@ -267,25 +278,28 @@ static BlockDriver *find_image_format(const char 
*filename)
        recognized as a host CDROM */
     if (strstart(filename, "/dev/cdrom", NULL))
         return &bdrv_host_device;
+    drv = find_protocol(filename);
+
+    if (drv == &bdrv_raw) {
 #ifdef _WIN32
-    if (is_windows_drive(filename))
-        return &bdrv_host_device;
+               if (is_windows_drive(filename))
+                       return &bdrv_host_device;
 #else
-    {
-        struct stat st;
-        if (stat(filename, &st) >= 0 &&
-            (S_ISCHR(st.st_mode) || S_ISBLK(st.st_mode))) {
-            return &bdrv_host_device;
-        }
-    }
+               {
+                       struct stat st;
+                       if (stat(filename, &st) >= 0 &&
+                               (S_ISCHR(st.st_mode) || S_ISBLK(st.st_mode))) {
+                                       return &bdrv_host_device;
+                               }
+               }
 #endif
+    }
 
-    drv = find_protocol(filename);
     /* no need to test disk image formats for vvfat */
     if (drv == &bdrv_vvfat)
         return drv;
 
-    ret = bdrv_file_open(&bs, filename, BDRV_O_RDONLY);
+    ret = bdrv_file_open(&bs, raw_filename(filename), BDRV_O_RDONLY);
     if (ret < 0)
         return NULL;
     ret = bdrv_pread(bs, 0, buf, sizeof(buf));
@@ -335,6 +349,7 @@ int bdrv_open2(BlockDriverState *bs, const char *filename, 
int flags,
     int ret, open_flags;
     char tmp_filename[PATH_MAX];
     char backing_filename[PATH_MAX];
+    char const *_filename;
 
     bs->read_only = 0;
     bs->is_temporary = 0;
@@ -403,9 +418,12 @@ int bdrv_open2(BlockDriverState *bs, const char *filename, 
int flags,
         open_flags = BDRV_O_RDWR | (flags & BDRV_O_CACHE_MASK);
     else
         open_flags = flags & ~(BDRV_O_FILE | BDRV_O_SNAPSHOT);
-    ret = drv->bdrv_open(bs, filename, open_flags);
+    
+    _filename = raw_filename(filename);
+
+    ret = drv->bdrv_open(bs, _filename, open_flags);
     if ((ret == -EACCES || ret == -EPERM) && !(flags & BDRV_O_FILE)) {
-        ret = drv->bdrv_open(bs, filename, open_flags & ~BDRV_O_RDWR);
+        ret = drv->bdrv_open(bs, _filename, open_flags & ~BDRV_O_RDWR);
         bs->read_only = 1;
     }
     if (ret < 0) {
diff --git a/qemu-img.c b/qemu-img.c