Merge series "filesystem visibility ioctls" of https://lore.kernel.org/r/20240207025624.1019754-1-kent.overstreet@linux.dev

Pull filesystem visibility ioctls series from Kent Overstreet:

This patch series adds a few new ioctls to standardize a few interfaces
to get and set filesystem uuid and retrieving the sysfs path.

The get UUID ioctls are lifted versions of the ext4 ioctls with one
difference, killing the flexible array member - we'll never have UUIDs
more than 16 bytes, and getting rid of the flexible array member makes
them easier to use.

FS_IOC_GETFSSYSFSPATH is new, but it addresses something that we've been
doing in fs specific code for awhile - "given a path on a mounted
filesystem, tell me where it lives in sysfs".

* series "filesystem visibility ioctls" of https://lore.kernel.org/r/20240207025624.1019754-1-kent.overstreet@linux.dev: (6 commits)
  xfs: add support for FS_IOC_GETFSSYSFSPATH
  fs: add FS_IOC_GETFSSYSFSPATH
  fat: Hook up sb->s_uuid
  fs: FS_IOC_GETUUID
  ovl: convert to super_set_uuid()
  fs: super_set_uuid()

Signed-off-by: Christian Brauner <brauner@kernel.org>

1 files changed, 52 insertions, 0 deletions

diff --git a/include/linux/fs.h b/include/linux/fs.h
index ed5966a70495..c6d9e1b7032c 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1255,8 +1255,22 @@ struct super_block {
 	struct fsnotify_mark_connector __rcu	*s_fsnotify_marks;
 #endif
 
+	/*
+	 * q: why are s_id and s_sysfs_name not the same? both are human
+	 * readable strings that identify the filesystem
+	 * a: s_id is allowed to change at runtime; it's used in log messages,
+	 * and we want to when a device starts out as single device (s_id is dev
+	 * name) but then a device is hot added and we have to switch to
+	 * identifying it by UUID
+	 * but s_sysfs_name is a handle for programmatic access, and can't
+	 * change at runtime
+	 */
 	char			s_id[32];	/* Informational name */
 	uuid_t			s_uuid;		/* UUID */
+	u8			s_uuid_len;	/* Default 16, possibly smaller for weird filesystems */
+
+	/* if set, fs shows up under sysfs at /sys/fs/$FSTYP/s_sysfs_name */
+	char			s_sysfs_name[UUID_STRING_LEN + 1];
 
 	unsigned int		s_max_links;
 
@@ -2532,6 +2546,44 @@ extern __printf(2, 3)
 int super_setup_bdi_name(struct super_block *sb, char *fmt, ...);
 extern int super_setup_bdi(struct super_block *sb);
 
+static inline void super_set_uuid(struct super_block *sb, const u8 *uuid, unsigned len)
+{
+	if (WARN_ON(len > sizeof(sb->s_uuid)))
+		len = sizeof(sb->s_uuid);
+	sb->s_uuid_len = len;
+	memcpy(&sb->s_uuid, uuid, len);
+}
+
+/* set sb sysfs name based on sb->s_bdev */
+static inline void super_set_sysfs_name_bdev(struct super_block *sb)
+{
+	snprintf(sb->s_sysfs_name, sizeof(sb->s_sysfs_name), "%pg", sb->s_bdev);
+}
+
+/* set sb sysfs name based on sb->s_uuid */
+static inline void super_set_sysfs_name_uuid(struct super_block *sb)
+{
+	WARN_ON(sb->s_uuid_len != sizeof(sb->s_uuid));
+	snprintf(sb->s_sysfs_name, sizeof(sb->s_sysfs_name), "%pU", sb->s_uuid.b);
+}
+
+/* set sb sysfs name based on sb->s_id */
+static inline void super_set_sysfs_name_id(struct super_block *sb)
+{
+	strscpy(sb->s_sysfs_name, sb->s_id, sizeof(sb->s_sysfs_name));
+}
+
+/* try to use something standard before you use this */
+__printf(2, 3)
+static inline void super_set_sysfs_name_generic(struct super_block *sb, const char *fmt, ...)
+{
+	va_list args;
+
+	va_start(args, fmt);
+	vsnprintf(sb->s_sysfs_name, sizeof(sb->s_sysfs_name), fmt, args);
+	va_end(args);
+}
+
 extern int current_umask(void);
 
 extern void ihold(struct inode * inode);