Expose whether snapdir is enabled

Include information about whether the ZFS snapdir is enabled
in the mount superblock information. This allows userspace
applications to use mountinfo to determine whether snapshots
will be accessible. The ability to specify snapdir or
nosnapdir as mount options is also added as a convenience
feature so that an admin may choose to temporarily override
the dataset property.

Signed-off-by: Andrew Walker <[email protected]>

Author: anodos325

include/os/linux/zfs/sys/zfs_vfsops_os.h

@@ -69,6 +69,8 @@ typedef struct vfs {
 	boolean_t	vfs_do_relatime;
 	boolean_t	vfs_nbmand;
 	boolean_t	vfs_do_nbmand;
+	boolean_t	vfs_snapdir;
+	boolean_t	vfs_do_snapdir;
 	kmutex_t	vfs_mntpt_lock;
 } vfs_t;
 

include/sys/mntent.h

@@ -111,5 +111,7 @@
 #define	MNTOPT_CASESENSITIVE	"casesensitive"		/* case sensitivity */
 #define	MNTOPT_CASEINSENSITIVE	"caseinsensitive"	/* case insensitivity */
 #define	MNTOPT_CASEMIXED	"casemixed"		/* case mixed */
+#define	MNTOPT_SNAPDIR		"snapdir"		/* hidden snapdir */
+#define	MNTOPT_NOSNAPDIR	"nosnapdir"		/* disabled snapdir */
 
 #endif	/* _SYS_MNTENT_H */

lib/libzfs/os/linux/libzfs_mount_os.c

@@ -91,6 +91,9 @@ static const option_map_t option_map[] = {
 	{ MNTOPT_CASESENSITIVE,		MS_COMMENT,	ZS_COMMENT	},
 	{ MNTOPT_CASEINSENSITIVE,	MS_COMMENT,	ZS_COMMENT	},
 	{ MNTOPT_CASEMIXED,		MS_COMMENT,	ZS_COMMENT	},
+	/* Snapdir options: snapdir == hidden, nosnapdir == disabled */
+	{ MNTOPT_SNAPDIR,	MS_COMMENT,	ZS_COMMENT	},
+	{ MNTOPT_NOSNAPDIR,	MS_COMMENT,	ZS_COMMENT	},
 #ifdef MS_NOATIME
 	{ MNTOPT_NOATIME,	MS_NOATIME,	ZS_COMMENT	},
 	{ MNTOPT_ATIME,		MS_COMMENT,	ZS_COMMENT	},

module/os/linux/zfs/zfs_vfsops.c

@@ -83,6 +83,8 @@ enum {
 	TOKEN_NBMAND,
 	TOKEN_NONBMAND,
 	TOKEN_MNTPOINT,
+	TOKEN_SNAPDIR,
+	TOKEN_NOSNAPDIR,
 	TOKEN_LAST,
 };
 
@@ -105,6 +107,8 @@ static const match_table_t zpl_tokens = {
 	{ TOKEN_NORELATIME,	MNTOPT_NORELATIME },
 	{ TOKEN_NBMAND,		MNTOPT_NBMAND },
 	{ TOKEN_NONBMAND,	MNTOPT_NONBMAND },
+	{ TOKEN_SNAPDIR,	MNTOPT_SNAPDIR },
+	{ TOKEN_NOSNAPDIR,	MNTOPT_NOSNAPDIR },
 	{ TOKEN_MNTPOINT,	MNTOPT_MNTPOINT "=%s" },
 	{ TOKEN_LAST,		NULL },
 };
@@ -196,6 +200,14 @@ zfsvfs_parse_option(char *option, int token, substring_t *args, vfs_t *vfsp)
 		vfsp->vfs_nbmand = B_FALSE;
 		vfsp->vfs_do_nbmand = B_TRUE;
 		break;
+	case TOKEN_SNAPDIR:
+		vfsp->vfs_snapdir = B_TRUE;
+		vfsp->vfs_do_snapdir = B_TRUE;
+		break;
+	case TOKEN_NOSNAPDIR:
+		vfsp->vfs_snapdir = B_FALSE;
+		vfsp->vfs_do_snapdir = B_TRUE;
+		break;
 	case TOKEN_MNTPOINT:
 		if (vfsp->vfs_mntpoint != NULL)
 			kmem_strfree(vfsp->vfs_mntpoint);
@@ -561,6 +573,9 @@ zfs_register_callbacks(vfs_t *vfsp)
 		relatime_changed_cb(zfsvfs, vfsp->vfs_relatime);
 	if (vfsp->vfs_do_nbmand)
 		nbmand_changed_cb(zfsvfs, vfsp->vfs_nbmand);
+	if (vfsp->vfs_do_snapdir)
+		snapdir_changed_cb(zfsvfs, vfsp->vfs_snapdir ?
+		   ZFS_SNAPDIR_HIDDEN : ZFS_SNAPDIR_DISABLED);
 
 	return (0);
 
@@ -633,6 +648,10 @@ zfs_get_temporary_prop(dsl_dataset_t *ds, zfs_prop_t zfs_prop, uint64_t *val,
 		if (vfsp->vfs_do_nbmand)
 			tmp = vfsp->vfs_nbmand;
 		break;
+	case ZFS_PROP_SNAPDIR:
+		if (vfsp->vfs_do_snapdir)
+			tmp = vfsp->vfs_snapdir;
+		break;
 	default:
 		return (ENOENT);
 	}

module/os/linux/zfs/zpl_super.c

@@ -240,6 +240,10 @@ __zpl_show_options(struct seq_file *seq, zfsvfs_t *zfsvfs)
 		break;
 	}
 
+	seq_printf(seq, ",%s",
+	    zfsvfs->z_show_ctldir == ZFS_SNAPDIR_DISABLED ?
+	    "nosnapdir" : "snapdir");
+
 	return (0);
 }