[PATCH v2] uimage: fix: add can_lseek_backward and use in uimage_open

[Sascha Hauer]

On Wed, Nov 08, 2017 at 07:07:47PM +0100, Michael Grzeschik wrote:
> Since commit ce0cc7fe we support forward seek on tftpfs. This feature
> breaks the condition to check rather we open an uimage over tftp. Since
> backward seeking is the problem here, we add the function
> can_lseek_backward and check for it instead of the simple lseek.
> 
> Signed-off-by: Michael Grzeschik <m.grzeschik at pengutronix.de>
> ---
> v1 -> v2: - added can_lseek_backward
>           - also fixed check in uimagefs
>           - aligned comments to check
> 
> common/uimage.c |  4 ++--
>  fs/uimagefs.c   |  4 ++--
>  include/fs.h    | 20 ++++++++++++++++++++
>  3 files changed, 24 insertions(+), 4 deletions(-)

Applied, thanks

Sascha

> 
> diff --git a/common/uimage.c b/common/uimage.c
> index 28a25bba2d..b6f0f109ca 100644
> --- a/common/uimage.c
> +++ b/common/uimage.c
> @@ -111,9 +111,9 @@ again:
>  	/*
>  	 * Hack around tftp fs. We need lseek for uImage support, but
>  	 * this cannot be implemented in tftp fs, so we detect this
> -	 * by doing a test lseek and copy the file to ram if it fails
> +	 * and copy the file to ram if it fails
>  	 */
> -	if (IS_BUILTIN(CONFIG_FS_TFTP) && lseek(fd, 0, SEEK_SET)) {
> +	if (IS_BUILTIN(CONFIG_FS_TFTP) && !can_lseek_backward(fd)) {
>  		close(fd);
>  		ret = copy_file(filename, uimage_tmp, 0);
>  		if (ret)
> diff --git a/fs/uimagefs.c b/fs/uimagefs.c
> index 13c1fbac05..c0c5750c2c 100644
> --- a/fs/uimagefs.c
> +++ b/fs/uimagefs.c
> @@ -374,9 +374,9 @@ again:
>  	/*
>  	 * Hack around tftp fs. We need lseek for uImage support, but
>  	 * this cannot be implemented in tftp fs, so we detect this
> -	 * by doing a test lseek and copy the file to ram if it fails
> +	 * and copy the file to ram if it fails
>  	 */
> -	if (IS_BUILTIN(CONFIG_FS_TFTP) && lseek(fd, 0, SEEK_SET)) {
> +	if (IS_BUILTIN(CONFIG_FS_TFTP) && !can_lseek_backward(fd)) {
>  		close(fd);
>  		ret = copy_file(priv->filename, priv->tmp, 0);
>  		if (ret)
> diff --git a/include/fs.h b/include/fs.h
> index d7fa7714b4..f8a3b8bda4 100644
> --- a/include/fs.h
> +++ b/include/fs.h
> @@ -100,6 +100,26 @@ struct fs_device_d {
>  	char *linux_rootarg;
>  };
>  
> +/*
> + * Some filesystems i.e. tftpfs only support lseek into one direction.
> + * To detect this limited functionality we add this extra function.
> + * Additionaly we also return 0 if we even can not seek forward.
> + */
> +static inline int can_lseek_backward(int fd)
> +{
> +	int ret;
> +
> +	ret = lseek(fd, 1, SEEK_SET);
> +	if (ret < 0)
> +		return 0;
> +
> +	ret = lseek(fd, 0, SEEK_SET);
> +	if (ret < 0)
> +		return 0;
> +
> +	return ret;
> +}
> +
>  #define drv_to_fs_driver(d) container_of(d, struct fs_driver_d, drv)
>  
>  int flush(int fd);
> -- 
> 2.11.0
> 
> 
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