vfs: Convert ramfs, shmem, tmpfs, devtmpfs, rootfs to use the new mount API

Convert the ramfs, shmem, tmpfs, devtmpfs and rootfs filesystems to the new
internal mount API as the old one will be obsoleted and removed.  This
allows greater flexibility in communication of mount parameters between
userspace, the VFS and the filesystem.

See Documentation/filesystems/mount_api.txt for more information.

Note that tmpfs is slightly tricky as it can contain embedded commas, so it
can't be trivially split up using strsep() to break on commas in
generic_parse_monolithic().  Instead, tmpfs has to supply its own generic
parser.

However, if tmpfs changes, then devtmpfs and rootfs, which are wrappers
around tmpfs or ramfs, must change too - and thus so must ramfs, so these
had to be converted also.

[AV: rewritten]

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Hugh Dickins <hughd@google.com>
cc: linux-mm@kvack.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 108 insertions, 79 deletions

diff --git a/mm/shmem.c b/mm/shmem.c
index 6a41595dd1b3..0f7fd4a85db6 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -3401,22 +3401,17 @@ const struct fs_parameter_description shmem_fs_parameters = {
 	.enums		= shmem_param_enums,
 };
 
-static int shmem_parse_one(struct shmem_options *ctx,
-			   struct fs_parameter *param)
+static int shmem_parse_one(struct fs_context *fc, struct fs_parameter *param)
 {
-	struct fs_context *fc = NULL;
+	struct shmem_options *ctx = fc->fs_private;
 	struct fs_parse_result result;
 	unsigned long long size;
 	char *rest;
 	int opt;
 
 	opt = fs_parse(fc, &shmem_fs_parameters, param, &result);
-	if (opt < 0) {
-		if (opt == -ENOPARAM)
-			return invalf(fc, "tmpfs: Unknown parameter '%s'",
-				      param->key);
+	if (opt < 0)
 		return opt;
-	}
 
 	switch (opt) {
 	case Opt_size:
@@ -3483,8 +3478,10 @@ bad_value:
 	return invalf(fc, "tmpfs: Bad value for '%s'", param->key);
 }
 
-static int shmem_parse_options(char *options, struct shmem_options *ctx)
+static int shmem_parse_options(struct fs_context *fc, void *data)
 {
+	char *options = data;
+
 	while (options != NULL) {
 		char *this_char = options;
 		for (;;) {
@@ -3504,85 +3501,81 @@ static int shmem_parse_options(char *options, struct shmem_options *ctx)
 		}
 		if (*this_char) {
 			char *value = strchr(this_char,'=');
-			struct fs_parameter param = {
-				.key	= this_char,
-				.type	= fs_value_is_string,
-			};
+			size_t len = 0;
 			int err;
 
 			if (value) {
 				*value++ = '\0';
-				param.size = strlen(value);
-				param.string = kstrdup(value, GFP_KERNEL);
-				if (!param.string)
-					goto error;
+				len = strlen(value);
 			}
-			err = shmem_parse_one(ctx, &param);
-			kfree(param.string);
-			if (err)
-				goto error;
+			err = vfs_parse_fs_string(fc, this_char, value, len);
+			if (err < 0)
+				return err;
 		}
 	}
 	return 0;
-
-error:
-	mpol_put(ctx->mpol);
-	ctx->mpol = NULL;
-	return 1;
-
 }
 
-static int shmem_remount_fs(struct super_block *sb, int *flags, char *data)
+/*
+ * Reconfigure a shmem filesystem.
+ *
+ * Note that we disallow change from limited->unlimited blocks/inodes while any
+ * are in use; but we must separately disallow unlimited->limited, because in
+ * that case we have no record of how much is already in use.
+ */
+static int shmem_reconfigure(struct fs_context *fc)
 {
-	struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
-	struct shmem_options ctx = {.seen = 0};
+	struct shmem_options *ctx = fc->fs_private;
+	struct shmem_sb_info *sbinfo = SHMEM_SB(fc->root->d_sb);
 	unsigned long inodes;
-	int error = -EINVAL;
-
-	if (shmem_parse_options(data, &ctx))
-		return error;
+	const char *err;
 
 	spin_lock(&sbinfo->stat_lock);
 	inodes = sbinfo->max_inodes - sbinfo->free_inodes;
-	/*
-	 * Those tests disallow limited->unlimited while any are in use;
-	 * but we must separately disallow unlimited->limited, because
-	 * in that case we have no record of how much is already in use.
-	 */
-	if ((ctx.seen & SHMEM_SEEN_BLOCKS) && ctx.blocks) {
-		if (!sbinfo->max_blocks)
+	if ((ctx->seen & SHMEM_SEEN_BLOCKS) && ctx->blocks) {
+		if (!sbinfo->max_blocks) {
+			err = "Cannot retroactively limit size";
 			goto out;
+		}
 		if (percpu_counter_compare(&sbinfo->used_blocks,
-					   ctx.blocks) > 0)
+					   ctx->blocks) > 0) {
+			err = "Too small a size for current use";
 			goto out;
+		}
 	}
-	if ((ctx.seen & SHMEM_SEEN_INODES) && ctx.inodes) {
-		if (!sbinfo->max_inodes)
+	if ((ctx->seen & SHMEM_SEEN_INODES) && ctx->inodes) {
+		if (!sbinfo->max_inodes) {
+			err = "Cannot retroactively limit inodes";
 			goto out;
-		if (ctx.inodes < inodes)
+		}
+		if (ctx->inodes < inodes) {
+			err = "Too few inodes for current use";
 			goto out;
+		}
 	}
 
-	error = 0;
-	if (ctx.seen & SHMEM_SEEN_HUGE)
-		sbinfo->huge = ctx.huge;
-	if (ctx.seen & SHMEM_SEEN_BLOCKS)
-		sbinfo->max_blocks  = ctx.blocks;
-	if (ctx.seen & SHMEM_SEEN_INODES) {
-		sbinfo->max_inodes  = ctx.inodes;
-		sbinfo->free_inodes = ctx.inodes - inodes;
+	if (ctx->seen & SHMEM_SEEN_HUGE)
+		sbinfo->huge = ctx->huge;
+	if (ctx->seen & SHMEM_SEEN_BLOCKS)
+		sbinfo->max_blocks  = ctx->blocks;
+	if (ctx->seen & SHMEM_SEEN_INODES) {
+		sbinfo->max_inodes  = ctx->inodes;
+		sbinfo->free_inodes = ctx->inodes - inodes;
 	}
 
 	/*
 	 * Preserve previous mempolicy unless mpol remount option was specified.
 	 */
-	if (ctx.mpol) {
+	if (ctx->mpol) {
 		mpol_put(sbinfo->mpol);
-		sbinfo->mpol = ctx.mpol;	/* transfers initial ref */
+		sbinfo->mpol = ctx->mpol;	/* transfers initial ref */
+		ctx->mpol = NULL;
 	}
+	spin_unlock(&sbinfo->stat_lock);
+	return 0;
 out:
 	spin_unlock(&sbinfo->stat_lock);
-	return error;
+	return invalf(fc, "tmpfs: %s", err);
 }
 
 static int shmem_show_options(struct seq_file *seq, struct dentry *root)
@@ -3623,13 +3616,11 @@ static void shmem_put_super(struct super_block *sb)
 	sb->s_fs_info = NULL;
 }
 
-static int shmem_fill_super(struct super_block *sb, void *data, int silent)
+static int shmem_fill_super(struct super_block *sb, struct fs_context *fc)
 {
+	struct shmem_options *ctx = fc->fs_private;
 	struct inode *inode;
 	struct shmem_sb_info *sbinfo;
-	struct shmem_options ctx = {.mode = 0777 | S_ISVTX,
-				    .uid = current_fsuid(),
-				    .gid = current_fsgid()};
 	int err = -ENOMEM;
 
 	/* Round up to L1_CACHE_BYTES to resist false sharing */
@@ -3647,12 +3638,10 @@ static int shmem_fill_super(struct super_block *sb, void *data, int silent)
 	 * but the internal instance is left unlimited.
 	 */
 	if (!(sb->s_flags & SB_KERNMOUNT)) {
-		ctx.blocks = shmem_default_max_blocks();
-		ctx.inodes = shmem_default_max_inodes();
-		if (shmem_parse_options(data, &ctx)) {
-			err = -EINVAL;
-			goto failed;
-		}
+		if (!(ctx->seen & SHMEM_SEEN_BLOCKS))
+			ctx->blocks = shmem_default_max_blocks();
+		if (!(ctx->seen & SHMEM_SEEN_INODES))
+			ctx->inodes = shmem_default_max_inodes();
 	} else {
 		sb->s_flags |= SB_NOUSER;
 	}
@@ -3661,13 +3650,14 @@ static int shmem_fill_super(struct super_block *sb, void *data, int silent)
 #else
 	sb->s_flags |= SB_NOUSER;
 #endif
-	sbinfo->max_blocks = ctx.blocks;
-	sbinfo->free_inodes = sbinfo->max_inodes = ctx.inodes;
-	sbinfo->uid = ctx.uid;
-	sbinfo->gid = ctx.gid;
-	sbinfo->mode = ctx.mode;
-	sbinfo->huge = ctx.huge;
-	sbinfo->mpol = ctx.mpol;
+	sbinfo->max_blocks = ctx->blocks;
+	sbinfo->free_inodes = sbinfo->max_inodes = ctx->inodes;
+	sbinfo->uid = ctx->uid;
+	sbinfo->gid = ctx->gid;
+	sbinfo->mode = ctx->mode;
+	sbinfo->huge = ctx->huge;
+	sbinfo->mpol = ctx->mpol;
+	ctx->mpol = NULL;
 
 	spin_lock_init(&sbinfo->stat_lock);
 	if (percpu_counter_init(&sbinfo->used_blocks, 0, GFP_KERNEL))
@@ -3704,6 +3694,31 @@ failed:
 	return err;
 }
 
+static int shmem_get_tree(struct fs_context *fc)
+{
+	return get_tree_nodev(fc, shmem_fill_super);
+}
+
+static void shmem_free_fc(struct fs_context *fc)
+{
+	struct shmem_options *ctx = fc->fs_private;
+
+	if (ctx) {
+		mpol_put(ctx->mpol);
+		kfree(ctx);
+	}
+}
+
+static const struct fs_context_operations shmem_fs_context_ops = {
+	.free			= shmem_free_fc,
+	.get_tree		= shmem_get_tree,
+#ifdef CONFIG_TMPFS
+	.parse_monolithic	= shmem_parse_options,
+	.parse_param		= shmem_parse_one,
+	.reconfigure		= shmem_reconfigure,
+#endif
+};
+
 static struct kmem_cache *shmem_inode_cachep;
 
 static struct inode *shmem_alloc_inode(struct super_block *sb)
@@ -3820,7 +3835,6 @@ static const struct super_operations shmem_ops = {
 	.destroy_inode	= shmem_destroy_inode,
 #ifdef CONFIG_TMPFS
 	.statfs		= shmem_statfs,
-	.remount_fs	= shmem_remount_fs,
 	.show_options	= shmem_show_options,
 #endif
 	.evict_inode	= shmem_evict_inode,
@@ -3841,16 +3855,30 @@ static const struct vm_operations_struct shmem_vm_ops = {
 #endif
 };
 
-struct dentry *shmem_mount(struct file_system_type *fs_type,
-	int flags, const char *dev_name, void *data)
+int shmem_init_fs_context(struct fs_context *fc)
 {
-	return mount_nodev(fs_type, flags, data, shmem_fill_super);
+	struct shmem_options *ctx;
+
+	ctx = kzalloc(sizeof(struct shmem_options), GFP_KERNEL);
+	if (!ctx)
+		return -ENOMEM;
+
+	ctx->mode = 0777 | S_ISVTX;
+	ctx->uid = current_fsuid();
+	ctx->gid = current_fsgid();
+
+	fc->fs_private = ctx;
+	fc->ops = &shmem_fs_context_ops;
+	return 0;
 }
 
 static struct file_system_type shmem_fs_type = {
 	.owner		= THIS_MODULE,
 	.name		= "tmpfs",
-	.mount		= shmem_mount,
+	.init_fs_context = shmem_init_fs_context,
+#ifdef CONFIG_TMPFS
+	.parameters	= &shmem_fs_parameters,
+#endif
 	.kill_sb	= kill_litter_super,
 	.fs_flags	= FS_USERNS_MOUNT,
 };
@@ -3994,7 +4022,8 @@ bool shmem_huge_enabled(struct vm_area_struct *vma)
 
 static struct file_system_type shmem_fs_type = {
 	.name		= "tmpfs",
-	.mount		= ramfs_mount,
+	.init_fs_context = ramfs_init_fs_context,
+	.parameters	= &ramfs_fs_parameters,
 	.kill_sb	= kill_litter_super,
 	.fs_flags	= FS_USERNS_MOUNT,
 };