tmpfs,xattr: enable limited user extended attributes

Enable "user." extended attributes on tmpfs, limiting them by tracking
the space they occupy, and deducting that space from the limited ispace
(unless tmpfs mounted with nr_inodes=0 to leave that ispace unlimited).

tmpfs inodes and simple xattrs are both unswappable, and have to be in
lowmem on a 32-bit highmem kernel: so the ispace limit is appropriate
for xattrs, without any need for a further mount option.

Add simple_xattr_space() to give approximate but deterministic estimate
of the space taken up by each xattr: with simple_xattrs_free() outputting
the space freed if required (but kernfs and even some tmpfs usages do not
require that, so don't waste time on strlen'ing if not needed).

Security and trusted xattrs were already supported: for consistency and
simplicity, account them from the same pool; though there's a small risk
that a tmpfs with enough space before would now be considered too small.

When extended attributes are used, "df -i" does show more IUsed and less
IFree than can be explained by the inodes: document that (manpage later).

xfstests tests/generic which were not run on tmpfs before but now pass:
020 037 062 070 077 097 103 117 337 377 454 486 523 533 611 618 728
with no new failures.

Signed-off-by: Hugh Dickins <hughd@google.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>
Message-Id: <2e63b26e-df46-5baa-c7d6-f9a8dd3282c5@google.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

1 files changed, 69 insertions, 9 deletions

diff --git a/mm/shmem.c b/mm/shmem.c
index 8c8f0b1b700c..ca43fb256b8e 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -393,12 +393,12 @@ static int shmem_reserve_inode(struct super_block *sb, ino_t *inop)
 	return 0;
 }
 
-static void shmem_free_inode(struct super_block *sb)
+static void shmem_free_inode(struct super_block *sb, size_t freed_ispace)
 {
 	struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
 	if (sbinfo->max_inodes) {
 		raw_spin_lock(&sbinfo->stat_lock);
-		sbinfo->free_ispace += BOGO_INODE_SIZE;
+		sbinfo->free_ispace += BOGO_INODE_SIZE + freed_ispace;
 		raw_spin_unlock(&sbinfo->stat_lock);
 	}
 }
@@ -1232,6 +1232,7 @@ static void shmem_evict_inode(struct inode *inode)
 {
 	struct shmem_inode_info *info = SHMEM_I(inode);
 	struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
+	size_t freed = 0;
 
 	if (shmem_mapping(inode->i_mapping)) {
 		shmem_unacct_size(info->flags, inode->i_size);
@@ -1258,9 +1259,9 @@ static void shmem_evict_inode(struct inode *inode)
 		}
 	}
 
-	simple_xattrs_free(&info->xattrs);
+	simple_xattrs_free(&info->xattrs, sbinfo->max_inodes ? &freed : NULL);
+	shmem_free_inode(inode->i_sb, freed);
 	WARN_ON(inode->i_blocks);
-	shmem_free_inode(inode->i_sb);
 	clear_inode(inode);
 #ifdef CONFIG_TMPFS_QUOTA
 	dquot_free_inode(inode);
@@ -2440,7 +2441,7 @@ static struct inode *__shmem_get_inode(struct mnt_idmap *idmap,
 	inode = new_inode(sb);
 
 	if (!inode) {
-		shmem_free_inode(sb);
+		shmem_free_inode(sb, 0);
 		return ERR_PTR(-ENOSPC);
 	}
 
@@ -3284,7 +3285,7 @@ static int shmem_link(struct dentry *old_dentry, struct inode *dir, struct dentr
 	ret = simple_offset_add(shmem_get_offset_ctx(dir), dentry);
 	if (ret) {
 		if (inode->i_nlink)
-			shmem_free_inode(inode->i_sb);
+			shmem_free_inode(inode->i_sb, 0);
 		goto out;
 	}
 
@@ -3304,7 +3305,7 @@ static int shmem_unlink(struct inode *dir, struct dentry *dentry)
 	struct inode *inode = d_inode(dentry);
 
 	if (inode->i_nlink > 1 && !S_ISDIR(inode->i_mode))
-		shmem_free_inode(inode->i_sb);
+		shmem_free_inode(inode->i_sb, 0);
 
 	simple_offset_remove(shmem_get_offset_ctx(dir), dentry);
 
@@ -3557,21 +3558,40 @@ static int shmem_initxattrs(struct inode *inode,
 			    void *fs_info)
 {
 	struct shmem_inode_info *info = SHMEM_I(inode);
+	struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
 	const struct xattr *xattr;
 	struct simple_xattr *new_xattr;
+	size_t ispace = 0;
 	size_t len;
 
+	if (sbinfo->max_inodes) {
+		for (xattr = xattr_array; xattr->name != NULL; xattr++) {
+			ispace += simple_xattr_space(xattr->name,
+				xattr->value_len + XATTR_SECURITY_PREFIX_LEN);
+		}
+		if (ispace) {
+			raw_spin_lock(&sbinfo->stat_lock);
+			if (sbinfo->free_ispace < ispace)
+				ispace = 0;
+			else
+				sbinfo->free_ispace -= ispace;
+			raw_spin_unlock(&sbinfo->stat_lock);
+			if (!ispace)
+				return -ENOSPC;
+		}
+	}
+
 	for (xattr = xattr_array; xattr->name != NULL; xattr++) {
 		new_xattr = simple_xattr_alloc(xattr->value, xattr->value_len);
 		if (!new_xattr)
-			return -ENOMEM;
+			break;
 
 		len = strlen(xattr->name) + 1;
 		new_xattr->name = kmalloc(XATTR_SECURITY_PREFIX_LEN + len,
 					  GFP_KERNEL);
 		if (!new_xattr->name) {
 			kvfree(new_xattr);
-			return -ENOMEM;
+			break;
 		}
 
 		memcpy(new_xattr->name, XATTR_SECURITY_PREFIX,
@@ -3582,6 +3602,16 @@ static int shmem_initxattrs(struct inode *inode,
 		simple_xattr_add(&info->xattrs, new_xattr);
 	}
 
+	if (xattr->name != NULL) {
+		if (ispace) {
+			raw_spin_lock(&sbinfo->stat_lock);
+			sbinfo->free_ispace += ispace;
+			raw_spin_unlock(&sbinfo->stat_lock);
+		}
+		simple_xattrs_free(&info->xattrs, NULL);
+		return -ENOMEM;
+	}
+
 	return 0;
 }
 
@@ -3602,16 +3632,39 @@ static int shmem_xattr_handler_set(const struct xattr_handler *handler,
 				   size_t size, int flags)
 {
 	struct shmem_inode_info *info = SHMEM_I(inode);
+	struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
 	struct simple_xattr *old_xattr;
+	size_t ispace = 0;
 
 	name = xattr_full_name(handler, name);
+	if (value && sbinfo->max_inodes) {
+		ispace = simple_xattr_space(name, size);
+		raw_spin_lock(&sbinfo->stat_lock);
+		if (sbinfo->free_ispace < ispace)
+			ispace = 0;
+		else
+			sbinfo->free_ispace -= ispace;
+		raw_spin_unlock(&sbinfo->stat_lock);
+		if (!ispace)
+			return -ENOSPC;
+	}
+
 	old_xattr = simple_xattr_set(&info->xattrs, name, value, size, flags);
 	if (!IS_ERR(old_xattr)) {
+		ispace = 0;
+		if (old_xattr && sbinfo->max_inodes)
+			ispace = simple_xattr_space(old_xattr->name,
+						    old_xattr->size);
 		simple_xattr_free(old_xattr);
 		old_xattr = NULL;
 		inode->i_ctime = current_time(inode);
 		inode_inc_iversion(inode);
 	}
+	if (ispace) {
+		raw_spin_lock(&sbinfo->stat_lock);
+		sbinfo->free_ispace += ispace;
+		raw_spin_unlock(&sbinfo->stat_lock);
+	}
 	return PTR_ERR(old_xattr);
 }
 
@@ -3627,9 +3680,16 @@ static const struct xattr_handler shmem_trusted_xattr_handler = {
 	.set = shmem_xattr_handler_set,
 };
 
+static const struct xattr_handler shmem_user_xattr_handler = {
+	.prefix = XATTR_USER_PREFIX,
+	.get = shmem_xattr_handler_get,
+	.set = shmem_xattr_handler_set,
+};
+
 static const struct xattr_handler *shmem_xattr_handlers[] = {
 	&shmem_security_xattr_handler,
 	&shmem_trusted_xattr_handler,
+	&shmem_user_xattr_handler,
 	NULL
 };