[Qemu-devel] Re: [PATCH] vvfat mbr fixes

[Lorenzo Campedelli]

Johannes Schindelin wrote:
> Hi,
>
> On Sun, 23 Sep 2007, Lorenzo Campedelli wrote:
>
> > While you are working on vvfat issues, could you give a look to the 
> > attached small patch?
>
> Okay, this is what I would do:
>
> - not make this handling dependent on vvfat (but this means checking if 
>   the colon is the second character, because then it is most likely 
>   a Windows path and does _not_ want special handling), and
>
> - I'd use the result of strrchr() directly.
>
> This is a sketch of the code I propose:
>
>         const char *tmp;
>
>         ...
>
>         get_tmp_filename(tmp_filename, sizeof(tmp_filename));
>         /* Handle 'fat:rw:<filename>' */
>         tmp = strrchr(backing_filename, ':');
>         if (tmp - backing_filename == 2) /* DOS path */
>                 tmp = NULL;
>         else if (tmp - backing_filename > 2 && tmp[-2] == ':')
>                 tmp -= 2;
>         realpath(filename, tmp ? tmp : backing_filename);
>
> Ciao,
> Dscho
Hi Johannes,

thanks for your reply. I gave another try at the patch.

I was concerned by having this handling outside of a proper
place (i.e. block-vvfat.c), but if we want to leave it there,
wouldn't it be better to just handle cases which would otherwise
fail, and just try to fix the "fat:" format?

The attached patch only tries to fix things when realpath() fails
to find a match and when the filename starts with a "fat:" header.

This way if anybody really wanted to use an image file named "fat:foo"
could do it without us handling it as a vvfat directory...

The code to handle the search for ':' and the DOS drive name special
case is stolen from block-vvfat.c, so you should like it ;-).

Regards,
Lorenzo

--- qemu-0.9.0.20070921/block.c.orig    2007-09-23 17:04:21.000000000 +0200
+++ qemu-0.9.0.20070921/block.c 2007-09-23 17:18:39.000000000 +0200
@@ -349,7 +349,19 @@
         bdrv_delete(bs1);
 
         get_tmp_filename(tmp_filename, sizeof(tmp_filename));
-        realpath(filename, backing_filename);
+        if (realpath(filename, backing_filename) == NULL) {
+            if (strstart(filename, "fat:", NULL)) {
+                int i = strrchr(filename, ':') - filename;
+
+                if ((filename[i-2] == ':') && isalpha(filename[i-1]))
+                    i -= 1; /* workaround for DOS drive names */
+                else
+                    i += 1;
+
+                strncpy(backing_filename, filename, i);
+                realpath(filename + i, backing_filename + i);
+            }
+        }
         if (bdrv_create(&bdrv_qcow2, tmp_filename,
                         total_size, backing_filename, 0) < 0) {
             return -1;