xattr: extract simple_xattr code from tmpfs

Extract in-memory xattr APIs from tmpfs. Will be used by cgroup.

$ size vmlinux.o
   text    data     bss     dec     hex filename
4658782  880729 5195032 10734543         a3cbcf vmlinux.o
$ size vmlinux.o
   text    data     bss     dec     hex filename
4658957  880729 5195032 10734718         a3cc7e vmlinux.o

v7:
- checkpatch warnings fixed
- Implement the changes requested by Hugh Dickins:
	- make simple_xattrs_init and simple_xattrs_free inline
	- get rid of locking and list reinitialization in simple_xattrs_free,
	  they're not needed
v6:
- no changes
v5:
- no changes
v4:
- move simple_xattrs_free() to fs/xattr.c
v3:
- in kmem_xattrs_free(), reinitialize the list
- use simple_xattr_* prefix
- introduce simple_xattr_add() to prevent direct list usage

Original-patch-by: Li Zefan <lizefan@huawei.com>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Hillf Danton <dhillf@gmail.com>
Cc: Lennart Poettering <lpoetter@redhat.com>
Acked-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Li Zefan <lizefan@huawei.com>
Signed-off-by: Aristeu Rozanski <aris@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

fs/xattr.c

@@ -791,3 +791,169 @@ EXPORT_SYMBOL(generic_getxattr);
 EXPORT_SYMBOL(generic_listxattr);
 EXPORT_SYMBOL(generic_setxattr);
 EXPORT_SYMBOL(generic_removexattr);
+
+/*
+ * Allocate new xattr and copy in the value; but leave the name to callers.
+ */
+struct simple_xattr *simple_xattr_alloc(const void *value, size_t size)
+{
+	struct simple_xattr *new_xattr;
+	size_t len;
+
+	/* wrap around? */
+	len = sizeof(*new_xattr) + size;
+	if (len <= sizeof(*new_xattr))
+		return NULL;
+
+	new_xattr = kmalloc(len, GFP_KERNEL);
+	if (!new_xattr)
+		return NULL;
+
+	new_xattr->size = size;
+	memcpy(new_xattr->value, value, size);
+	return new_xattr;
+}
+
+/*
+ * xattr GET operation for in-memory/pseudo filesystems
+ */
+int simple_xattr_get(struct simple_xattrs *xattrs, const char *name,
+		     void *buffer, size_t size)
+{
+	struct simple_xattr *xattr;
+	int ret = -ENODATA;
+
+	spin_lock(&xattrs->lock);
+	list_for_each_entry(xattr, &xattrs->head, list) {
+		if (strcmp(name, xattr->name))
+			continue;
+
+		ret = xattr->size;
+		if (buffer) {
+			if (size < xattr->size)
+				ret = -ERANGE;
+			else
+				memcpy(buffer, xattr->value, xattr->size);
+		}
+		break;
+	}
+	spin_unlock(&xattrs->lock);
+	return ret;
+}
+
+static int __simple_xattr_set(struct simple_xattrs *xattrs, const char *name,
+			      const void *value, size_t size, int flags)
+{
+	struct simple_xattr *xattr;
+	struct simple_xattr *new_xattr = NULL;
+	int err = 0;
+
+	/* value == NULL means remove */
+	if (value) {
+		new_xattr = simple_xattr_alloc(value, size);
+		if (!new_xattr)
+			return -ENOMEM;
+
+		new_xattr->name = kstrdup(name, GFP_KERNEL);
+		if (!new_xattr->name) {
+			kfree(new_xattr);
+			return -ENOMEM;
+		}
+	}
+
+	spin_lock(&xattrs->lock);
+	list_for_each_entry(xattr, &xattrs->head, list) {
+		if (!strcmp(name, xattr->name)) {
+			if (flags & XATTR_CREATE) {
+				xattr = new_xattr;
+				err = -EEXIST;
+			} else if (new_xattr) {
+				list_replace(&xattr->list, &new_xattr->list);
+			} else {
+				list_del(&xattr->list);
+			}
+			goto out;
+		}
+	}
+	if (flags & XATTR_REPLACE) {
+		xattr = new_xattr;
+		err = -ENODATA;
+	} else {
+		list_add(&new_xattr->list, &xattrs->head);
+		xattr = NULL;
+	}
+out:
+	spin_unlock(&xattrs->lock);
+	if (xattr) {
+		kfree(xattr->name);
+		kfree(xattr);
+	}
+	return err;
+
+}
+
+/*
+ * xattr SET operation for in-memory/pseudo filesystems
+ */
+int simple_xattr_set(struct simple_xattrs *xattrs, const char *name,
+		     const void *value, size_t size, int flags)
+{
+	if (size == 0)
+		value = ""; /* empty EA, do not remove */
+	return __simple_xattr_set(xattrs, name, value, size, flags);
+}
+
+/*
+ * xattr REMOVE operation for in-memory/pseudo filesystems
+ */
+int simple_xattr_remove(struct simple_xattrs *xattrs, const char *name)
+{
+	return __simple_xattr_set(xattrs, name, NULL, 0, XATTR_REPLACE);
+}
+
+static bool xattr_is_trusted(const char *name)
+{
+	return !strncmp(name, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN);
+}
+
+/*
+ * xattr LIST operation for in-memory/pseudo filesystems
+ */
+ssize_t simple_xattr_list(struct simple_xattrs *xattrs, char *buffer,
+			  size_t size)
+{
+	bool trusted = capable(CAP_SYS_ADMIN);
+	struct simple_xattr *xattr;
+	size_t used = 0;
+
+	spin_lock(&xattrs->lock);
+	list_for_each_entry(xattr, &xattrs->head, list) {
+		size_t len;
+
+		/* skip "trusted." attributes for unprivileged callers */
+		if (!trusted && xattr_is_trusted(xattr->name))
+			continue;
+
+		len = strlen(xattr->name) + 1;
+		used += len;
+		if (buffer) {
+			if (size < used) {
+				used = -ERANGE;
+				break;
+			}
+			memcpy(buffer, xattr->name, len);
+			buffer += len;
+		}
+	}
+	spin_unlock(&xattrs->lock);
+
+	return used;
+}
+
+void simple_xattr_list_add(struct simple_xattrs *xattrs,
+			   struct simple_xattr *new_xattr)
+{
+	spin_lock(&xattrs->lock);
+	list_add(&new_xattr->list, &xattrs->head);
+	spin_unlock(&xattrs->lock);
+}

include/linux/shmem_fs.h

@@ -5,6 +5,7 @@
 #include <linux/mempolicy.h>
 #include <linux/pagemap.h>
 #include <linux/percpu_counter.h>
+#include <linux/xattr.h>
 
 /* inode in-kernel data */
 
@@ -18,7 +19,7 @@ struct shmem_inode_info {
 	};
 	struct shared_policy	policy;		/* NUMA memory alloc policy */
 	struct list_head	swaplist;	/* chain of maybes on swap */
-	struct list_head	xattr_list;	/* list of shmem_xattr */
+	struct simple_xattrs	xattrs;		/* list of xattrs */
 	struct inode		vfs_inode;
 };
 

include/linux/xattr.h

@@ -59,7 +59,9 @@
 
 #ifdef  __KERNEL__
 
+#include <linux/slab.h>
 #include <linux/types.h>
+#include <linux/spinlock.h>
 
 struct inode;
 struct dentry;
@@ -96,6 +98,52 @@ ssize_t vfs_getxattr_alloc(struct dentry *dentry, const char *name,
 			   char **xattr_value, size_t size, gfp_t flags);
 int vfs_xattr_cmp(struct dentry *dentry, const char *xattr_name,
 		  const char *value, size_t size, gfp_t flags);
+
+struct simple_xattrs {
+	struct list_head head;
+	spinlock_t lock;
+};
+
+struct simple_xattr {
+	struct list_head list;
+	char *name;
+	size_t size;
+	char value[0];
+};
+
+/*
+ * initialize the simple_xattrs structure
+ */
+static inline void simple_xattrs_init(struct simple_xattrs *xattrs)
+{
+	INIT_LIST_HEAD(&xattrs->head);
+	spin_lock_init(&xattrs->lock);
+}
+
+/*
+ * free all the xattrs
+ */
+static inline void simple_xattrs_free(struct simple_xattrs *xattrs)
+{
+	struct simple_xattr *xattr, *node;
+
+	list_for_each_entry_safe(xattr, node, &xattrs->head, list) {
+		kfree(xattr->name);
+		kfree(xattr);
+	}
+}
+
+struct simple_xattr *simple_xattr_alloc(const void *value, size_t size);
+int simple_xattr_get(struct simple_xattrs *xattrs, const char *name,
+		     void *buffer, size_t size);
+int simple_xattr_set(struct simple_xattrs *xattrs, const char *name,
+		     const void *value, size_t size, int flags);
+int simple_xattr_remove(struct simple_xattrs *xattrs, const char *name);
+ssize_t simple_xattr_list(struct simple_xattrs *xattrs, char *buffer,
+			  size_t size);
+void simple_xattr_list_add(struct simple_xattrs *xattrs,
+			   struct simple_xattr *new_xattr);
+
 #endif  /*  __KERNEL__  */
 
 #endif	/* _LINUX_XATTR_H */

mm/shmem.c

@@ -77,13 +77,6 @@ static struct vfsmount *shm_mnt;
 /* Symlink up to this size is kmalloc'ed instead of using a swappable page */
 #define SHORT_SYMLINK_LEN 128
 
-struct shmem_xattr {
-	struct list_head list;	/* anchored by shmem_inode_info->xattr_list */
-	char *name;		/* xattr name */
-	size_t size;
-	char value[0];
-};
-
 /*
  * shmem_fallocate and shmem_writepage communicate via inode->i_private
  * (with i_mutex making sure that it has only one user at a time):
@@ -636,7 +629,6 @@ static int shmem_setattr(struct dentry *dentry, struct iattr *attr)
 static void shmem_evict_inode(struct inode *inode)
 {
 	struct shmem_inode_info *info = SHMEM_I(inode);
-	struct shmem_xattr *xattr, *nxattr;
 
 	if (inode->i_mapping->a_ops == &shmem_aops) {
 		shmem_unacct_size(info->flags, inode->i_size);
@@ -650,10 +642,7 @@ static void shmem_evict_inode(struct inode *inode)
 	} else
 		kfree(info->symlink);
 
-	list_for_each_entry_safe(xattr, nxattr, &info->xattr_list, list) {
-		kfree(xattr->name);
-		kfree(xattr);
-	}
+	simple_xattrs_free(&info->xattrs);
 	BUG_ON(inode->i_blocks);
 	shmem_free_inode(inode->i_sb);
 	clear_inode(inode);
@@ -1377,7 +1366,7 @@ static struct inode *shmem_get_inode(struct super_block *sb, const struct inode
 		spin_lock_init(&info->lock);
 		info->flags = flags & VM_NORESERVE;
 		INIT_LIST_HEAD(&info->swaplist);
-		INIT_LIST_HEAD(&info->xattr_list);
+		simple_xattrs_init(&info->xattrs);
 		cache_no_acl(inode);
 
 		switch (mode & S_IFMT) {
@@ -2059,28 +2048,6 @@ static void shmem_put_link(struct dentry *dentry, struct nameidata *nd, void *co
  * filesystem level, though.
  */
 
-/*
- * Allocate new xattr and copy in the value; but leave the name to callers.
- */
-static struct shmem_xattr *shmem_xattr_alloc(const void *value, size_t size)
-{
-	struct shmem_xattr *new_xattr;
-	size_t len;
-
-	/* wrap around? */
-	len = sizeof(*new_xattr) + size;
-	if (len <= sizeof(*new_xattr))
-		return NULL;
-
-	new_xattr = kmalloc(len, GFP_KERNEL);
-	if (!new_xattr)
-		return NULL;
-
-	new_xattr->size = size;
-	memcpy(new_xattr->value, value, size);
-	return new_xattr;
-}
-
 /*
  * Callback for security_inode_init_security() for acquiring xattrs.
  */
@@ -2090,11 +2057,11 @@ static int shmem_initxattrs(struct inode *inode,
 {
 	struct shmem_inode_info *info = SHMEM_I(inode);
 	const struct xattr *xattr;
-	struct shmem_xattr *new_xattr;
+	struct simple_xattr *new_xattr;
 	size_t len;
 
 	for (xattr = xattr_array; xattr->name != NULL; xattr++) {
-		new_xattr = shmem_xattr_alloc(xattr->value, xattr->value_len);
+		new_xattr = simple_xattr_alloc(xattr->value, xattr->value_len);
 		if (!new_xattr)
 			return -ENOMEM;
 
@@ -2111,91 +2078,12 @@ static int shmem_initxattrs(struct inode *inode,
 		memcpy(new_xattr->name + XATTR_SECURITY_PREFIX_LEN,
 		       xattr->name, len);
 
-		spin_lock(&info->lock);
-		list_add(&new_xattr->list, &info->xattr_list);
-		spin_unlock(&info->lock);
+		simple_xattr_list_add(&info->xattrs, new_xattr);
 	}
 
 	return 0;
 }
 
-static int shmem_xattr_get(struct dentry *dentry, const char *name,
-			   void *buffer, size_t size)
-{
-	struct shmem_inode_info *info;
-	struct shmem_xattr *xattr;
-	int ret = -ENODATA;
-
-	info = SHMEM_I(dentry->d_inode);
-
-	spin_lock(&info->lock);
-	list_for_each_entry(xattr, &info->xattr_list, list) {
-		if (strcmp(name, xattr->name))
-			continue;
-
-		ret = xattr->size;
-		if (buffer) {
-			if (size < xattr->size)
-				ret = -ERANGE;
-			else
-				memcpy(buffer, xattr->value, xattr->size);
-		}
-		break;
-	}
-	spin_unlock(&info->lock);
-	return ret;
-}
-
-static int shmem_xattr_set(struct inode *inode, const char *name,
-			   const void *value, size_t size, int flags)
-{
-	struct shmem_inode_info *info = SHMEM_I(inode);
-	struct shmem_xattr *xattr;
-	struct shmem_xattr *new_xattr = NULL;
-	int err = 0;
-
-	/* value == NULL means remove */
-	if (value) {
-		new_xattr = shmem_xattr_alloc(value, size);
-		if (!new_xattr)
-			return -ENOMEM;
-
-		new_xattr->name = kstrdup(name, GFP_KERNEL);
-		if (!new_xattr->name) {
-			kfree(new_xattr);
-			return -ENOMEM;
-		}
-	}
-
-	spin_lock(&info->lock);
-	list_for_each_entry(xattr, &info->xattr_list, list) {
-		if (!strcmp(name, xattr->name)) {
-			if (flags & XATTR_CREATE) {
-				xattr = new_xattr;
-				err = -EEXIST;
-			} else if (new_xattr) {
-				list_replace(&xattr->list, &new_xattr->list);
-			} else {
-				list_del(&xattr->list);
-			}
-			goto out;
-		}
-	}
-	if (flags & XATTR_REPLACE) {
-		xattr = new_xattr;
-		err = -ENODATA;
-	} else {
-		list_add(&new_xattr->list, &info->xattr_list);
-		xattr = NULL;
-	}
-out:
-	spin_unlock(&info->lock);
-	if (xattr)
-		kfree(xattr->name);
-	kfree(xattr);
-	return err;
-}
-
 static const struct xattr_handler *shmem_xattr_handlers[] = {
 #ifdef CONFIG_TMPFS_POSIX_ACL
 	&generic_acl_access_handler,
@@ -2226,6 +2114,7 @@ static int shmem_xattr_validate(const char *name)
 static ssize_t shmem_getxattr(struct dentry *dentry, const char *name,
 			      void *buffer, size_t size)
 {
+	struct shmem_inode_info *info = SHMEM_I(dentry->d_inode);
 	int err;
 
 	/*
@@ -2240,12 +2129,13 @@ static ssize_t shmem_getxattr(struct dentry *dentry, const char *name,
 	if (err)
 		return err;
 
-	return shmem_xattr_get(dentry, name, buffer, size);
+	return simple_xattr_get(&info->xattrs, name, buffer, size);
 }
 
 static int shmem_setxattr(struct dentry *dentry, const char *name,
 			  const void *value, size_t size, int flags)
 {
+	struct shmem_inode_info *info = SHMEM_I(dentry->d_inode);
 	int err;
 
 	/*
@@ -2260,15 +2150,12 @@ static int shmem_setxattr(struct dentry *dentry, const char *name,
 	if (err)
 		return err;
 
-	if (size == 0)
-		value = "";  /* empty EA, do not remove */
-
-	return shmem_xattr_set(dentry->d_inode, name, value, size, flags);
-
+	return simple_xattr_set(&info->xattrs, name, value, size, flags);
 }
 
 static int shmem_removexattr(struct dentry *dentry, const char *name)
 {
+	struct shmem_inode_info *info = SHMEM_I(dentry->d_inode);
 	int err;
 
 	/*
@@ -2283,45 +2170,13 @@ static int shmem_removexattr(struct dentry *dentry, const char *name)
 	if (err)
 		return err;
 
-	return shmem_xattr_set(dentry->d_inode, name, NULL, 0, XATTR_REPLACE);
-}
-
-static bool xattr_is_trusted(const char *name)
-{
-	return !strncmp(name, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN);
+	return simple_xattr_remove(&info->xattrs, name);
 }
 
 static ssize_t shmem_listxattr(struct dentry *dentry, char *buffer, size_t size)
 {
-	bool trusted = capable(CAP_SYS_ADMIN);
-	struct shmem_xattr *xattr;
-	struct shmem_inode_info *info;
-	size_t used = 0;
-
-	info = SHMEM_I(dentry->d_inode);
-
-	spin_lock(&info->lock);
-	list_for_each_entry(xattr, &info->xattr_list, list) {
-		size_t len;
-
-		/* skip "trusted." attributes for unprivileged callers */
-		if (!trusted && xattr_is_trusted(xattr->name))
-			continue;
-
-		len = strlen(xattr->name) + 1;
-		used += len;
-		if (buffer) {
-			if (size < used) {
-				used = -ERANGE;
-				break;
-			}
-			memcpy(buffer, xattr->name, len);
-			buffer += len;
-		}
-	}
-	spin_unlock(&info->lock);
-
-	return used;
+	struct shmem_inode_info *info = SHMEM_I(dentry->d_inode);
+	return simple_xattr_list(&info->xattrs, buffer, size);
 }
 #endif /* CONFIG_TMPFS_XATTR */