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statmount: add flag to retrieve unescaped options

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Filesystem options can be retrieved with STATMOUNT_MNT_OPTS, which
returns a string of comma separated options, where some characters are
escaped using the \OOO notation.

Add a new flag, STATMOUNT_OPT_ARRAY, which instead returns the raw
option values separated with '\0' charaters.

Since escaped charaters are rare, this inteface is preferable for
non-libmount users which likley don't want to deal with option
de-escaping.

Example code:

	if (st->mask & STATMOUNT_OPT_ARRAY) {
		const char *opt = st->str + st->opt_array;

		for (unsigned int i = 0; i < st->opt_num; i++) {
			printf("opt_array[%i]: <%s>\n", i, opt);
			opt += strlen(opt) + 1;
		}
	}

Example ouput:

(1) mnt_opts: <lowerdir+=/l\054w\054r,lowerdir+=/l\054w\054r1,upperdir=/upp\054r,workdir=/w\054rk,redirect_dir=nofollow,uuid=null>

(2) opt_array[0]: <lowerdir+=/l,w,r>
    opt_array[1]: <lowerdir+=/l,w,r1>
    opt_array[2]: <upperdir=/upp,r>
    opt_array[3]: <workdir=/w,rk>
    opt_array[4]: <redirect_dir=nofollow>
    opt_array[5]: <uuid=null>

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Link: https://lore.kernel.org/r/20241112101006.30715-1-mszeredi@redhat.com
Acked-by: Jeff Layton <jlayton@kernel.org>
[brauner: tweak variable naming and parsing add example output]
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Miklos Szeredi
2024-11-12 11:10:04 +01:00
committed by Christian Brauner
parent 39bb1bf0b4
commit 2f4d4503e9
2 changed files with 51 additions and 3 deletions
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7
include/uapi/linux/mount.h
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@@ -154,7 +154,7 @@ struct mount_attr {
*/
struct statmount {
__u32 size; /* Total size, including strings */
__u32 mnt_opts; /* [str] Mount options of the mount */
__u32 mnt_opts; /* [str] Options (comma separated, escaped) */
__u64 mask; /* What results were written */
__u32 sb_dev_major; /* Device ID */
__u32 sb_dev_minor;
@@ -175,7 +175,9 @@ struct statmount {
__u64 mnt_ns_id; /* ID of the mount namespace */
__u32 fs_subtype; /* [str] Subtype of fs_type (if any) */
__u32 sb_source; /* [str] Source string of the mount */
__u64 __spare2[48];
__u32 opt_num; /* Number of fs options */
__u32 opt_array; /* [str] Array of nul terminated fs options */
__u64 __spare2[47];
char str[]; /* Variable size part containing strings */
};
@@ -211,6 +213,7 @@ struct mnt_id_req {
#define STATMOUNT_MNT_OPTS 0x00000080U /* Want/got mnt_opts */
#define STATMOUNT_FS_SUBTYPE 0x00000100U /* Want/got fs_subtype */
#define STATMOUNT_SB_SOURCE 0x00000200U /* Want/got sb_source */
#define STATMOUNT_OPT_ARRAY 0x00000400U /* Want/got opt_... */
/*
* Special @mnt_id values that can be passed to listmount