Re: [Qemu-devel] [PATCH 3/3] make path_combine() especially for filenames, not URLs

[Kevin Wolf <kwolf@redhat.com>]

Am 12.01.2011 11:57, schrieb Michael Tokarev:
> Currently the two routines tries to "understand" and skip <protocol>:
> prefix in path arguments are path_combine() and path_is_absolute()
> (the latter isn't used anywhere but in the former).  This is wrong,
> since notion of absolute path is, at least, protocol-specific.
> 
> The implementation is more wrong on windows where even non-absolute
> paths but with drive name (d:foo) should be treated as absolute, as
> in, one can't combine, say, c:\bar with d:foo forming c:\foo as
> path_combine() currently does.
> 
> Introduce isslash() macro that works correctly on both windows and
> unix, use it in is_windows_drive_prefix() (since any form of slash
> can be used in constructs like //./), 

You're saying that \/.\ is a valid format for it? Wow...

> remove path_is_absolute() and
> hardcode the trivial (but right) condition in path_combine(), and
> simplify path_combine() further by removing <protocol>: handling
> and unifying shash searching.
> 
> Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
> ---
>  block.c |   72 +++++++++++++++++++++-----------------------------------------
>  1 files changed, 25 insertions(+), 47 deletions(-)
> 
> diff --git a/block.c b/block.c
> index 42d6ff1..31a821d 100644
> --- a/block.c
> +++ b/block.c
> @@ -71,6 +71,9 @@ static BlockDriverState *bs_snapshots;
>  static int use_bdrv_whitelist;
>  
>  #ifdef _WIN32
> +
> +#define isslash(c) ((c) == '/' || (c) == '\\')
> +
>  static int is_windows_drive_prefix(const char *filename)
>  {
>      return (((filename[0] >= 'a' && filename[0] <= 'z') ||
> @@ -83,11 +86,17 @@ int is_windows_drive(const char *filename)
>      if (is_windows_drive_prefix(filename) &&
>          filename[2] == '\0')
>          return 1;
> -    if (strstart(filename, "\\\\.\\", NULL) ||
> -        strstart(filename, "//./", NULL))
> -        return 1;
> +    if (isslash(filename[0] && isslash(filename[1]) &&

Missing bracket, doesn't even compile.

> +        filename[2] == '.' &&  isslash(filename[3]))
> +        return 1; /* special case: windows device "//./" */

Please add curly braces.

>      return 0;
>  }
> +
> +#else
> +
> +#define isslash(c) ((c) == '/')
> +#define is_windows_drive_prefix(filename) (0)

Please make this a function, for consistency and type checking. The
compiler is going to inline it anyway.

> +
>  #endif
>  
>  /* check if the path starts with "<protocol>:"
> @@ -115,61 +124,30 @@ static char *path_has_protocol(const char *path)
>              (char*)p : NULL;
>  }
>  
> -int path_is_absolute(const char *path)
> -{
> -    const char *p;
> -#ifdef _WIN32
> -    /* specific case for names like: "\\.\d:" */
> -    if (*path == '/' || *path == '\\')
> -        return 1;
> -#endif
> -    p = strchr(path, ':');
> -    if (p)
> -        p++;
> -    else
> -        p = path;
> -#ifdef _WIN32
> -    return (*p == '/' || *p == '\\');
> -#else
> -    return (*p == '/');
> -#endif
> -}
> -
>  /* if filename is absolute, just copy it to dest. Otherwise, build a
> -   path to it by considering it is relative to base_path. URL are
> -   supported. */
> +   path to it by considering it is relative to base_path.
> +   This is really about filenames not URLs - we don't support
> +   <protocol>: prefix in filename since it makes no sense, especially
> +   if the protocol in base_path is not the same as in filename.
> + */
>  void path_combine(char *dest, int dest_size,
>                    const char *base_path,
>                    const char *filename)
>  {
> -    const char *p, *p1;
> +    const char *p;
>      int len;
>  
>      if (dest_size <= 0)
>          return;
> -    if (path_is_absolute(filename)) {
> +    /* on windows, d:filename should be treated as absolute too */
> +    if (isslash(filename[0]) || is_windows_drive_prefix(filename)) {
>          pstrcpy(dest, dest_size, filename);
>      } else {
> -        p = strchr(base_path, ':');
> -        if (p)
> -            p++;
> -        else
> -            p = base_path;
> -        p1 = strrchr(base_path, '/');
> -#ifdef _WIN32
> -        {
> -            const char *p2;
> -            p2 = strrchr(base_path, '\\');
> -            if (!p1 || p2 > p1)
> -                p1 = p2;
> -        }
> -#endif
> -        if (p1)
> -            p1++;
> -        else
> -            p1 = base_path;
> -        if (p1 > p)
> -            p = p1;
> +        /* find last slash */
> +        p = base_path + strlen(base_path);
> +        while(p >= base_path && !isslash(*p))
> +            --p;
> +        p++;

Please add braces.

>          len = p - base_path;
>          if (len > dest_size - 1)
>              len = dest_size - 1;

This changes the semantics to throw away the protocol. For example
fat:foo combined with bar would have resulted in fat:bar previously  and
results in bar now.

Probably not a problem. path_combine gets even worse if filename has a
protocol. It's completely unclear what it's supposed to do with
protocols anyway.

Kevin