[LTP] [PATCH v2] syscalls/ioctl_loop05: Use correct blockdev to get logical_block_size

[Jan Stancek <jstancek@redhat.com>]

----- Original Message -----
> 
> Using df cmd (df -T /tmp/xxxxx/test.img)to get the correct block dev.

What I had in mind was to take "df -T" as inspiration, not call it directly,
but that could work too. See notes below.

> +static void find_backing_bdpath(char *buf)
> +{
> +	char line[PATH_MAX];
> +	FILE *file;
> +
> +	file = SAFE_FOPEN("1.txt", "r");
> +
> +	while (fgets(line, sizeof(line), file) != NULL)
> +		sscanf(line, "%s", buf);

This will take the last line of output, which can be a problem as some
version align output differently. For example:

# df -T .
Filesystem           Type 1K-blocks    Used Available Use% Mounted on
/dev/mapper/vg_dhcp13579-lv_root
                     ext4  46967160 3102232  41472456   7% /

can break output into two lines.

> +	SAFE_FCLOSE(file);
> +}
> +
>  static void setup(void)
>  {
> -	int fd;
> -	struct stat buf;
> +	char buf[100];
> +	const char *const df_cmd[] = {"df", "-T", ".", NULL};
>  
>  	if (tst_fs_type(".") == TST_TMPFS_MAGIC)
>  		tst_brk(TCONF, "tmpfd doesn't support O_DIRECT flag");
> @@ -109,13 +122,6 @@ static void setup(void)
>  	sprintf(sys_loop_diopath, "/sys/block/loop%d/loop/dio", dev_num);
>  	tst_fill_file("test.img", 0, 1024, 1024);
>  
> -	fd = SAFE_OPEN("test.img", O_RDONLY);
> -	SAFE_FSTAT(fd, &buf);
> -	SAFE_CLOSE(fd);
> -
> -	logical_block_size = buf.st_blksize;
> -	tst_res(TINFO, "backing dev logical_block_size is %d", logical_block_size);
> -
>  	tst_attach_device(dev_path, "test.img");
>  	attach_flag = 1;
>  	dev_fd = SAFE_OPEN(dev_path, O_RDWR);
> @@ -130,13 +136,24 @@ static void setup(void)
>  	 *   size of loop is bigger than the backing device's and the loop
>  	 *   needn't transform transfer.
>  	 */
> -	TST_RETRY_FUNC(ioctl(dev_fd, LOOP_SET_BLOCK_SIZE, logical_block_size),
> TST_RETVAL_EQ0);
> +	SAFE_CMD(df_cmd, "1.txt", NULL);

This could be part of find_backing_bdpath() function.

What I had in mind when I referred to df was something like:
  stat("test.img", &statbuf);
  SAFE_MKNOD("blkdev", S_IFBLK | S_IRWXU, statbuf.st_dev);
  block_devfd = SAFE_OPEN("blkdev", O_RDWR);
What do you think?