[Qemu-devel] [PATCH] qemu-img: adding a "-F base_fmt" option to "qemu-img create -b"

[uril@redhat.com]

From: Uri Lublin <uril@redhat.com>

If the user specifies the backing file format,
then when opening the backing file, there is no need
to probe the (backing file) image to figure out its format.

This follows my previous patch implementing fmt:FMT: prefix for backing
filename.

Suggested by Daniel P. Berrange.

Signed-off-by: Uri Lublin <uril@redhat.com>
---
 qemu-img.c    |   31 ++++++++++++++++++++++++++++---
 qemu-img.texi |    4 +++-
 2 files changed, 31 insertions(+), 4 deletions(-)

diff --git a/qemu-img.c b/qemu-img.c
index 964b28b..02c513f 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -25,6 +25,7 @@
 #include "osdep.h"
 #include "block_int.h"
 #include <assert.h>
+#include <stdio.h>
 
 #ifdef _WIN32
 #define WIN32_LEAN_AND_MEAN
@@ -57,7 +58,7 @@ static void help(void)
            "QEMU disk image utility\n"
            "\n"
            "Command syntax:\n"
-           "  create [-e] [-6] [-b base_image] [-f fmt] filename [size]\n"
+           "  create [-e] [-6] [-F fmt] [-b base_image] [-f fmt] filename [size]\n"
            "  commit [-f fmt] filename\n"
            "  convert [-c] [-e] [-6] [-f fmt] [-O output_fmt] [-B output_base_image] filename [filename2 [...]] output_filename\n"
            "  info [-f fmt] filename\n"
@@ -215,21 +216,26 @@ static int img_create(int argc, char **argv)
 {
     int c, ret, flags;
     const char *fmt = "raw";
+    const char *base_fmt = NULL;
     const char *filename;
     const char *base_filename = NULL;
     uint64_t size;
     const char *p;
     BlockDriver *drv;
+    char filename_buff[1024];
 
     flags = 0;
     for(;;) {
-        c = getopt(argc, argv, "b:f:he6");
+        c = getopt(argc, argv, "F:b:f:he6");
         if (c == -1)
             break;
         switch(c) {
         case 'h':
             help();
             break;
+        case 'F':
+            base_fmt = optarg;
+            break;
         case 'b':
             base_filename = optarg;
             break;
@@ -250,7 +256,15 @@ static int img_create(int argc, char **argv)
     size = 0;
     if (base_filename) {
         BlockDriverState *bs;
-        bs = bdrv_new_open(base_filename, NULL);
+        BlockDriver *base_drv = NULL;
+        
+        if (base_fmt) {
+            base_drv = bdrv_find_format(base_fmt);
+            if (base_drv == NULL)
+                error("Unknown basefile format '%s'", base_fmt);
+        }
+        
+        bs = bdrv_new_open(base_filename, base_fmt);
         bdrv_get_geometry(bs, &size);
         size *= 512;
         bdrv_delete(bs);
@@ -281,8 +295,19 @@ static int img_create(int argc, char **argv)
     if (base_filename) {
         printf(", backing_file=%s",
                base_filename);
+        if (base_fmt)
+            printf(", backing_fmt=%s",
+                   base_fmt);
     }
     printf(", size=%" PRIu64 " kB\n", size / 1024);
+    if (base_filename && base_fmt) {
+        int len;
+        len = snprintf(filename_buff, sizeof(filename_buff), "fmt:%s:%s", 
+                       base_fmt, base_filename);
+        if (len < 0)
+            error("internal failure: snprintf failed");
+        base_filename = filename_buff;
+    }
     ret = bdrv_create(drv, filename, size / 512, base_filename, flags);
     if (ret < 0) {
         if (ret == -ENOTSUP) {
diff --git a/qemu-img.texi b/qemu-img.texi
index 1c0504b..eaeaf07 100644
--- a/qemu-img.texi
+++ b/qemu-img.texi
@@ -8,7 +8,7 @@ usage: qemu-img command [command options]
 
 The following commands are supported:
 @table @option
-@item create [-e] [-6] [-b @var{base_image}] [-f @var{fmt}] @var{filename} [@var{size}]
+@item create [-e] [-6] [-F @var{base_fmt}] [-b @var{base_image}] [-f @var{fmt}] @var{filename} [@var{size}]
 @item commit [-f @var{fmt}] @var{filename}
 @item convert [-c] [-e] [-6] [-f @var{fmt}] [-O @var{output_fmt}] [-B @var{output_base_image}] @var{filename} [@var{filename2} [...]] @var{output_filename}
 @item info [-f @var{fmt}] @var{filename}
@@ -26,6 +26,8 @@ forces the output image to be created as a copy on write
 image of the specified base image; @code{output_base_image} should have the same
 content as the input's base image, however the path, image format, etc may
 differ
+@item base_fmt
+is the disk image format of @var{base_image}. for more information look at @var{fmt}
 @item fmt
 is the disk image format. It is guessed automatically in most cases. The following formats are supported:
 
-- 
1.6.0.6