Re: [PATCH 06/10] example/single_file: take no sector size from a regular backing file

["Darrick J. Wong" <djwong@kernel.org>]

On Fri, Sep 25, 2026 at 12:23:34AM +0200, Bernd Schubert via B4 Relay wrote:
> From: Bernd Schubert <bernd@bsbernd.com>
> 
> single_file_configure() took the sector size of a regular backing file
> from st_blksize, and refused to start when it was larger than the page
> size. For a regular file st_blksize is only a preferred I/O size, and
> the file is not opened with O_DIRECT, so any offset works. NFS reports
> 1 MiB there, so service_ll and service_hl failed on an image on NFS
> with "lba size 1048576 smaller than blocksize 4096".
> 
> Assisted-by: LLM
> Signed-off-by: Bernd Schubert <bernd@bsbernd.com>
> ---
>  example/single_file.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/example/single_file.c b/example/single_file.c
> index 59dbc6bbac5e..4260ecf3c5f5 100644
> --- a/example/single_file.c
> +++ b/example/single_file.c
> @@ -887,7 +887,8 @@ int single_file_configure(const char *device, const char *filename)
>  		perror(device);
>  		return -1;
>  	}
> -	lbasize = stbuf.st_blksize;
> +	/* A regular file takes any offset; its st_blksize is only an I/O hint */
> +	lbasize = S_ISBLK(stbuf.st_mode) ? stbuf.st_blksize : 1;

You could just flow that into the S_ISBLK clause below, but I don't feel
strongly either way.  The justification is reasonable so
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

--D


>  	backing_size = stbuf.st_size;
>  
>  	if (S_ISBLK(stbuf.st_mode)) {
> 
> -- 
> 2.53.0
> 
> 
>