[Libguestfs] [PATCH] fuse: resolve absolute links to relative ones

[Richard W.M. Jones]

On Wed, Mar 18, 2015 at 02:21:31PM +0100, Maros Zatko wrote:
> First it strips /sysroot and then finds common prefix aligned
> on slashes. Next it produces ../ for each slash found in common
> prefix and concatenates them with the rest of resolved link.
> 
> Fixes RHBZ#604041
> ---
>  src/fuse.c | 33 ++++++++++++++++++++++++++++++++-
>  1 file changed, 32 insertions(+), 1 deletion(-)
> 
> diff --git a/src/fuse.c b/src/fuse.c
> index 3fdb1d4..6c7eee1 100644
> --- a/src/fuse.c
> +++ b/src/fuse.c
> @@ -386,7 +386,38 @@ mount_local_readlink (const char *path, char *buf, size_t size)
>    if (len > size - 1)
>      len = size - 1;
>  
> -  memcpy (buf, r, len);
> +  buf[0] = '\0';
> +  size_t offset = 0;
> +  if (STRPREFIX (r, "/sysroot")) {
> +    offset = strlen ("/sysroot") + 1;
> +    size_t i;
> +    for (i = 0; (i < strlen (r+offset)) && (path[i] == r[i+offset-1]); i++);
> +    /* Now i contains index where paths starts to differ
> +     * (n.b. needs to be aligned on last slash). */
> +
> +    for (; path[i] != '/'; --i);
> +    /* i is now aligned */
> +
> +    /* Count slashes in original path, so we can generate
> +     * right amount of ../ */
> +    size_t j; int cnt = 0;
> +    for (j = i+1; j < strlen (r+offset); j++) {
> +      if (path[j] == '/') cnt++;
> +    }
> +
> +    /* For each slash create ../ in path */
> +    for (int z = 0; z < cnt; z++) {
> +      strcat (buf, "../");
> +    }
> +
> +    /* In addition to /sysroot ne need to remove common path
> +     * aligned on slashes */
> +    offset += i;
> +  }
> +
> +  /* There might already be something in buf (such as ../)
> +   * so let's concatenate the rest of path */
> +  strncat (buf, r + offset, len - offset + 1);
>    buf[len] = '\0';

This makes my head hurt.  Perhaps some diagrams or examples
of how this is supposed to work?

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
virt-df lists disk usage of guests without needing to install any
software inside the virtual machine.  Supports Linux and Windows.
http://people.redhat.com/~rjones/virt-df/