[PATCH] losetup: Create loop device if it does not exist

[Joerg Vehlow]

No interest in util-linux compatibility?

Am 23.09.2019 um 07:39 schrieb Joerg Vehlow:
> From: Joerg Vehlow <joerg.vehlow at aox-tech.de>
>
> util-linux's losetup creates a loop device, if it is missing.
> This is missing in busybox's implementation.
>
> Testcase:
> losetup /dev/loop1000 <somepath>
> If /dev/loop1000 does not exist busybox give an error but
> util-linux's losetup just creates the file
>
> Signed-off-by: Joerg Vehlow <joerg.vehlow at aox-tech.de>
> ---
>   util-linux/losetup.c | 15 +++++++++++++++
>   1 file changed, 15 insertions(+)
>
> diff --git a/util-linux/losetup.c b/util-linux/losetup.c
> index cc6c2b1d5..790c41cab 100644
> --- a/util-linux/losetup.c
> +++ b/util-linux/losetup.c
> @@ -147,10 +147,25 @@ int losetup_main(int argc UNUSED_PARAM, char **argv)
>   			d = *argv++;
>   
>   		if (argv[0]) {
> +			struct stat statbuf;
> +			int n;
>   			unsigned flags = (opt & OPT_r) ?
> BB_LO_FLAGS_READ_ONLY : 0;
> +
>   			if (opt & OPT_P) {
>   				flags |= BB_LO_FLAGS_PARTSCAN;
>   			}
> +
> +			// If the loop device does not exist, create it
> +			if (stat(d, &statbuf) != 0 && errno == ENOENT) {
> +				if (sscanf(d, LOOP_FORMAT, &n) != 1) {
> +					errno = 0;
> +					bb_perror_msg_and_die("Loop device
> %s does not exist and does not start with " LOOP_NAME, d);
> +				}
> +				if (mknod(d, S_IFBLK|0644, makedev(7, n))
> != 0) {
> +					bb_simple_perror_msg_and_die(d);
> +				}
> +			}
> +
>   			if (set_loop(&d, argv[0], offset, flags) < 0)
>   				bb_simple_perror_msg_and_die(argv[0]);
>   			return EXIT_SUCCESS;