[Qemu-devel] [PATCH v2 0/2] block: Avoid second open for format probing

[Qemu-devel] [PATCH v2 0/2] block: Avoid second open for format probing

[Kevin Wolf]

Kevin Wolf (2):
  block: Factor out bdrv_open_flags
  block: Avoid second open for format probing

 block.c |  101 ++++++++++++++++++++++++++++++++++++--------------------------
 1 files changed, 59 insertions(+), 42 deletions(-)

-- 
1.7.6.5

[Qemu-devel] [PATCH v2 1/2] block: Factor out bdrv_open_flags

[Kevin Wolf]

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 block.c |   35 +++++++++++++++++++++--------------
 1 files changed, 21 insertions(+), 14 deletions(-)

diff --git a/block.c b/block.c
index bf0747f..95fd00e 100644
--- a/block.c
+++ b/block.c
@@ -634,6 +634,26 @@ void bdrv_disable_copy_on_read(BlockDriverState *bs)
     bs->copy_on_read--;
 }
 
+static int bdrv_open_flags(BlockDriverState *bs, int flags)
+{
+    int open_flags = flags | BDRV_O_CACHE_WB;
+
+    /*
+     * Clear flags that are internal to the block layer before opening the
+     * image.
+     */
+    open_flags &= ~(BDRV_O_SNAPSHOT | BDRV_O_NO_BACKING);
+
+    /*
+     * Snapshots should be writable.
+     */
+    if (bs->is_temporary) {
+        open_flags |= BDRV_O_RDWR;
+    }
+
+    return open_flags;
+}
+
 /*
  * Common part for opening disk images and files
  */
@@ -665,20 +685,7 @@ static int bdrv_open_common(BlockDriverState *bs, const char *filename,
     bs->opaque = g_malloc0(drv->instance_size);
 
     bs->enable_write_cache = !!(flags & BDRV_O_CACHE_WB);
-    open_flags = flags | BDRV_O_CACHE_WB;
-
-    /*
-     * Clear flags that are internal to the block layer before opening the
-     * image.
-     */
-    open_flags &= ~(BDRV_O_SNAPSHOT | BDRV_O_NO_BACKING);
-
-    /*
-     * Snapshots should be writable.
-     */
-    if (bs->is_temporary) {
-        open_flags |= BDRV_O_RDWR;
-    }
+    open_flags = bdrv_open_flags(bs, flags);
 
     bs->read_only = !(open_flags & BDRV_O_RDWR);
 
-- 
1.7.6.5

[Qemu-devel] [PATCH v2 2/2] block: Avoid second open for format probing

[Kevin Wolf]

This fixes problems that are caused by the additional open/close cycle
of the existing format probing, for example related to qemu-nbd without
-t option or file descriptor passing.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 block.c |   66 ++++++++++++++++++++++++++++++++++++--------------------------
 1 files changed, 38 insertions(+), 28 deletions(-)

diff --git a/block.c b/block.c
index 95fd00e..1be667f 100644
--- a/block.c
+++ b/block.c
@@ -518,22 +518,16 @@ BlockDriver *bdrv_find_protocol(const char *filename)
     return NULL;
 }
 
-static int find_image_format(const char *filename, BlockDriver **pdrv)
+static int find_image_format(BlockDriverState *bs, const char *filename,
+                             BlockDriver **pdrv)
 {
-    int ret, score, score_max;
+    int score, score_max;
     BlockDriver *drv1, *drv;
     uint8_t buf[2048];
-    BlockDriverState *bs;
-
-    ret = bdrv_file_open(&bs, filename, 0);
-    if (ret < 0) {
-        *pdrv = NULL;
-        return ret;
-    }
+    int ret = 0;
 
     /* Return the raw BlockDriver * to scsi-generic devices or empty drives */
     if (bs->sg || !bdrv_is_inserted(bs)) {
-        bdrv_delete(bs);
         drv = bdrv_find_format("raw");
         if (!drv) {
             ret = -ENOENT;
@@ -543,7 +537,6 @@ static int find_image_format(const char *filename, BlockDriver **pdrv)
     }
 
     ret = bdrv_pread(bs, 0, buf, sizeof(buf));
-    bdrv_delete(bs);
     if (ret < 0) {
         *pdrv = NULL;
         return ret;
@@ -657,7 +650,8 @@ static int bdrv_open_flags(BlockDriverState *bs, int flags)
 /*
  * Common part for opening disk images and files
  */
-static int bdrv_open_common(BlockDriverState *bs, const char *filename,
+static int bdrv_open_common(BlockDriverState *bs, BlockDriverState *file,
+    const char *filename,
     int flags, BlockDriver *drv)
 {
     int ret, open_flags;
@@ -691,12 +685,16 @@ static int bdrv_open_common(BlockDriverState *bs, const char *filename,
 
     /* Open the image, either directly or using a protocol */
     if (drv->bdrv_file_open) {
-        ret = drv->bdrv_file_open(bs, filename, open_flags);
-    } else {
-        ret = bdrv_file_open(&bs->file, filename, open_flags);
-        if (ret >= 0) {
-            ret = drv->bdrv_open(bs, open_flags);
+        if (file != NULL) {
+            bdrv_swap(file, bs);
+            ret = 0;
+        } else {
+            ret = drv->bdrv_file_open(bs, filename, open_flags);
         }
+    } else {
+        assert(file != NULL);
+        bs->file = file;
+        ret = drv->bdrv_open(bs, open_flags);
     }
 
     if (ret < 0) {
@@ -716,10 +714,7 @@ static int bdrv_open_common(BlockDriverState *bs, const char *filename,
     return 0;
 
 free_and_fail:
-    if (bs->file) {
-        bdrv_delete(bs->file);
-        bs->file = NULL;
-    }
+    bs->file = NULL;
     g_free(bs->opaque);
     bs->opaque = NULL;
     bs->drv = NULL;
@@ -741,7 +736,7 @@ int bdrv_file_open(BlockDriverState **pbs, const char *filename, int flags)
     }
 
     bs = bdrv_new("");
-    ret = bdrv_open_common(bs, filename, flags, drv);
+    ret = bdrv_open_common(bs, NULL, filename, flags, drv);
     if (ret < 0) {
         bdrv_delete(bs);
         return ret;
@@ -795,6 +790,7 @@ int bdrv_open(BlockDriverState *bs, const char *filename, int flags,
 {
     int ret;
     char tmp_filename[PATH_MAX];
+    BlockDriverState *file = NULL;
 
     if (flags & BDRV_O_SNAPSHOT) {
         BlockDriverState *bs1;
@@ -854,25 +850,36 @@ int bdrv_open(BlockDriverState *bs, const char *filename, int flags,
         bs->is_temporary = 1;
     }
 
+    /* Open image file without format layer */
+    if (flags & BDRV_O_RDWR) {
+        flags |= BDRV_O_ALLOW_RDWR;
+    }
+
+    ret = bdrv_file_open(&file, filename, bdrv_open_flags(bs, flags));
+    if (ret < 0) {
+        return ret;
+    }
+
     /* Find the right image format driver */
     if (!drv) {
-        ret = find_image_format(filename, &drv);
+        ret = find_image_format(file, filename, &drv);
     }
 
     if (!drv) {
         goto unlink_and_fail;
     }
 
-    if (flags & BDRV_O_RDWR) {
-        flags |= BDRV_O_ALLOW_RDWR;
-    }
-
     /* Open the image */
-    ret = bdrv_open_common(bs, filename, flags, drv);
+    ret = bdrv_open_common(bs, file, filename, flags, drv);
     if (ret < 0) {
         goto unlink_and_fail;
     }
 
+    if (bs->file != file) {
+        bdrv_delete(file);
+        file = NULL;
+    }
+
     /* If there is a backing file, use it */
     if ((flags & BDRV_O_NO_BACKING) == 0) {
         ret = bdrv_open_backing_file(bs);
@@ -894,6 +901,9 @@ int bdrv_open(BlockDriverState *bs, const char *filename, int flags,
     return 0;
 
 unlink_and_fail:
+    if (file != NULL) {
+        bdrv_delete(file);
+    }
     if (bs->is_temporary) {
         unlink(filename);
     }
-- 
1.7.6.5

Re: [Qemu-devel] [PATCH v2 2/2] block: Avoid second open for format probing

[Stefan Hajnoczi]

On Thu, Nov 15, 2012 at 01:57:37PM +0100, Kevin Wolf wrote:
> This fixes problems that are caused by the additional open/close cycle
> of the existing format probing, for example related to qemu-nbd without
> -t option or file descriptor passing.
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  block.c |   66 ++++++++++++++++++++++++++++++++++++--------------------------
>  1 files changed, 38 insertions(+), 28 deletions(-)

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>