[Libguestfs] [PATCH] lib: create: avoid one extra string allocation

[Richard W.M. Jones]

On Wed, Aug 22, 2018 at 04:57:17PM +0200, Pino Toscano wrote:
> When creating the qemu-img command, use the guestfs_int_cmd_add_arg &
> guestfs_int_cmd_add_arg_format APIs to add the proper filename directly,
> without creating a string for it.
> 
> This should cause no functional change.
> ---
>  lib/create.c | 25 +++++++++++--------------
>  1 file changed, 11 insertions(+), 14 deletions(-)
> 
> diff --git a/lib/create.c b/lib/create.c
> index 60e467fb6..fcc5855e0 100644
> --- a/lib/create.c
> +++ b/lib/create.c
> @@ -250,11 +250,10 @@ is_power_of_2 (unsigned v)
>                                 VALID_FLAG_ALPHA|VALID_FLAG_DIGIT, "")
>  
>  static int
> -disk_create_qcow2 (guestfs_h *g, const char *orig_filename, int64_t size,
> +disk_create_qcow2 (guestfs_h *g, const char *filename, int64_t size,
>                     const char *backingfile,
>                     const struct guestfs_disk_create_argv *optargs)
>  {
> -  CLEANUP_FREE char *filename = NULL;
>    const char *backingformat = NULL;
>    const char *preallocation = NULL;
>    const char *compat = NULL;
> @@ -263,16 +262,6 @@ disk_create_qcow2 (guestfs_h *g, const char *orig_filename, int64_t size,
>    CLEANUP_CMD_CLOSE struct command *cmd = guestfs_int_new_command (g);
>    int r;
>  
> -  /* If the filename is something like "file:foo" then qemu-img will
> -   * try to interpret that as "foo" in the file:/// protocol.  To
> -   * avoid that, if the path is relative prefix it with "./" since
> -   * qemu-img won't try to interpret such a path.
> -   */
> -  if (orig_filename[0] != '/')
> -    filename = safe_asprintf (g, "./%s", orig_filename);
> -  else
> -    filename = safe_strdup (g, orig_filename);
> -
>    if (optargs->bitmask & GUESTFS_DISK_CREATE_BACKINGFORMAT_BITMASK) {
>      backingformat = optargs->backingformat;
>      if (!VALID_FORMAT (backingformat)) {
> @@ -341,13 +330,21 @@ disk_create_qcow2 (guestfs_h *g, const char *orig_filename, int64_t size,
>    }
>  
>    /* Complete the command line. */
> -  guestfs_int_cmd_add_arg (cmd, filename);
> +  /* If the filename is something like "file:foo" then qemu-img will
> +   * try to interpret that as "foo" in the file:/// protocol.  To
> +   * avoid that, if the path is relative prefix it with "./" since
> +   * qemu-img won't try to interpret such a path.
> +   */
> +  if (filename[0] == '/')
> +    guestfs_int_cmd_add_arg (cmd, filename);
> +  else
> +    guestfs_int_cmd_add_arg_format (cmd, "./%s", filename);
>    if (size >= 0)
>      guestfs_int_cmd_add_arg_format (cmd, "%" PRIi64, size);
>  
>    r = guestfs_int_cmd_run (cmd);
>    if (!WIFEXITED (r) || WEXITSTATUS (r) != 0) {
> -    guestfs_int_external_command_failed (g, r, "qemu-img", orig_filename);
> +    guestfs_int_external_command_failed (g, r, "qemu-img", filename);
>      return -1;
>    }

Seems sensible, ACK.

Rich.

-- 
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