[PATCH] Fix qemu-img can't create qcow image based on read-only image

[Sheng Yang <sheng@xxxxxxxxxxxxxxx>]

Commit 03cbdac7 "Disable fall-back to read-only when cannot open drive's
file for read-write" result in read-only image can't be used as backed
image in qemu-img.

CC: Naphtali Sprei <nsprei@xxxxxxxxxx>
Signed-off-by: Sheng Yang <sheng@xxxxxxxxxxxxxxx>
---

This issue blocked our QA's KVM nightly test. But in fact, I don't like this
patch, feeling uncomfortable to change long existed interface... Any
alternative? Add a readonly command line would change the default behavior(I
don't think fall back to readonly looks like a bug); or even revert the
commit? What's the story behind it?

 qemu-img.c |   15 ++++++++++-----
 1 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/qemu-img.c b/qemu-img.c
index 3cea8ce..f8be5cb 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -188,11 +188,13 @@ static int read_password(char *buf, int buf_size)
 #endif
 
 static BlockDriverState *bdrv_new_open(const char *filename,
-                                       const char *fmt)
+                                       const char *fmt,
+                                       int readonly)
 {
     BlockDriverState *bs;
     BlockDriver *drv;
     char password[256];
+    int flags = BRDV_O_FLAGS;
 
     bs = bdrv_new("");
     if (!bs)
@@ -204,7 +206,10 @@ static BlockDriverState *bdrv_new_open(const char *filename,
     } else {
         drv = NULL;
     }
-    if (bdrv_open2(bs, filename, BRDV_O_FLAGS | BDRV_O_RDWR, drv) < 0) {
+    if (!readonly) {
+        flags |= BDRV_O_RDWR;
+    }
+    if (bdrv_open2(bs, filename, flags, drv) < 0) {
         error("Could not open '%s'", filename);
     }
     if (bdrv_is_encrypted(bs)) {
@@ -343,7 +348,7 @@ static int img_create(int argc, char **argv)
                 }
             }
 
-            bs = bdrv_new_open(backing_file->value.s, fmt);
+            bs = bdrv_new_open(backing_file->value.s, fmt, 1);
             bdrv_get_geometry(bs, &size);
             size *= 512;
             bdrv_delete(bs);
@@ -627,7 +632,7 @@ static int img_convert(int argc, char **argv)
 
     total_sectors = 0;
     for (bs_i = 0; bs_i < bs_n; bs_i++) {
-        bs[bs_i] = bdrv_new_open(argv[optind + bs_i], fmt);
+        bs[bs_i] = bdrv_new_open(argv[optind + bs_i], fmt, 0);
         if (!bs[bs_i])
             error("Could not open '%s'", argv[optind + bs_i]);
         bdrv_get_geometry(bs[bs_i], &bs_sectors);
@@ -685,7 +690,7 @@ static int img_convert(int argc, char **argv)
         }
     }
 
-    out_bs = bdrv_new_open(out_filename, out_fmt);
+    out_bs = bdrv_new_open(out_filename, out_fmt, 0);
 
     bs_i = 0;
     bs_offset = 0;
-- 
1.5.4.5

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