vfs: move ACL cache lookup into generic code

This moves logic for checking the cached ACL values from low-level
filesystems into generic code.  The end result is a streamlined ACL
check that doesn't need to load the inode->i_op->check_acl pointer at
all for the common cached case.

The filesystems also don't need to check for a non-blocking RCU walk
case in their acl_check() functions, because that is all handled at a
VFS layer.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/9p/acl.c

@@ -101,9 +101,6 @@ int v9fs_check_acl(struct inode *inode, int mask)
 	struct posix_acl *acl;
 	struct v9fs_session_info *v9ses;
 
-	if (mask & MAY_NOT_BLOCK)
-		return -ECHILD;
-
 	v9ses = v9fs_inode2v9ses(inode);
 	if (((v9ses->flags & V9FS_ACCESS_MASK) != V9FS_ACCESS_CLIENT) ||
 			((v9ses->flags & V9FS_ACL_MASK) != V9FS_POSIX_ACL)) {

fs/btrfs/acl.c

@@ -198,19 +198,14 @@ out:
 int btrfs_check_acl(struct inode *inode, int mask)
 {
 	int error = -EAGAIN;
+	struct posix_acl *acl;
 
-	if (mask & MAY_NOT_BLOCK) {
-		if (!negative_cached_acl(inode, ACL_TYPE_ACCESS))
-			error = -ECHILD;
-	} else {
-		struct posix_acl *acl;
-		acl = btrfs_get_acl(inode, ACL_TYPE_ACCESS);
-		if (IS_ERR(acl))
-			return PTR_ERR(acl);
-		if (acl) {
-			error = posix_acl_permission(inode, acl, mask);
-			posix_acl_release(acl);
-		}
+	acl = btrfs_get_acl(inode, ACL_TYPE_ACCESS);
+	if (IS_ERR(acl))
+		return PTR_ERR(acl);
+	if (acl) {
+		error = posix_acl_permission(inode, acl, mask);
+		posix_acl_release(acl);
 	}
 
 	return error;

fs/ext2/acl.c

@@ -236,12 +236,6 @@ ext2_check_acl(struct inode *inode, int mask)
 {
 	struct posix_acl *acl;
 
-	if (mask & MAY_NOT_BLOCK) {
-		if (!negative_cached_acl(inode, ACL_TYPE_ACCESS))
-			return -ECHILD;
-		return -EAGAIN;
-	}
-
 	acl = ext2_get_acl(inode, ACL_TYPE_ACCESS);
 	if (IS_ERR(acl))
 		return PTR_ERR(acl);

fs/ext3/acl.c

@@ -244,12 +244,6 @@ ext3_check_acl(struct inode *inode, int mask)
 {
 	struct posix_acl *acl;
 
-	if (mask & MAY_NOT_BLOCK) {
-		if (!negative_cached_acl(inode, ACL_TYPE_ACCESS))
-			return -ECHILD;
-		return -EAGAIN;
-	}
-
 	acl = ext3_get_acl(inode, ACL_TYPE_ACCESS);
 	if (IS_ERR(acl))
 		return PTR_ERR(acl);

fs/ext4/acl.c

@@ -242,12 +242,6 @@ ext4_check_acl(struct inode *inode, int mask)
 {
 	struct posix_acl *acl;
 
-	if (mask & MAY_NOT_BLOCK) {
-		if (!negative_cached_acl(inode, ACL_TYPE_ACCESS))
-			return -ECHILD;
-		return -EAGAIN;
-	}
-
 	acl = ext4_get_acl(inode, ACL_TYPE_ACCESS);
 	if (IS_ERR(acl))
 		return PTR_ERR(acl);

fs/generic_acl.c

@@ -192,18 +192,13 @@ generic_acl_chmod(struct inode *inode)
 int
 generic_check_acl(struct inode *inode, int mask)
 {
-	if (mask & MAY_NOT_BLOCK) {
-		if (!negative_cached_acl(inode, ACL_TYPE_ACCESS))
-			return -ECHILD;
-	} else {
-		struct posix_acl *acl;
-
-		acl = get_cached_acl(inode, ACL_TYPE_ACCESS);
-		if (acl) {
-			int error = posix_acl_permission(inode, acl, mask);
-			posix_acl_release(acl);
-			return error;
-		}
+	struct posix_acl *acl;
+
+	acl = get_cached_acl(inode, ACL_TYPE_ACCESS);
+	if (acl) {
+		int error = posix_acl_permission(inode, acl, mask);
+		posix_acl_release(acl);
+		return error;
 	}
 	return -EAGAIN;
 }

fs/gfs2/acl.c

@@ -80,12 +80,6 @@ int gfs2_check_acl(struct inode *inode, int mask)
 	struct posix_acl *acl;
 	int error;
 
-	if (mask & MAY_NOT_BLOCK) {
-		if (!negative_cached_acl(inode, ACL_TYPE_ACCESS))
-			return -ECHILD;
-		return -EAGAIN;
-	}
-
 	acl = gfs2_acl_get(GFS2_I(inode), ACL_TYPE_ACCESS);
 	if (IS_ERR(acl))
 		return PTR_ERR(acl);

fs/jffs2/acl.c

@@ -264,9 +264,6 @@ int jffs2_check_acl(struct inode *inode, int mask)
 	struct posix_acl *acl;
 	int rc;
 
-	if (mask & MAY_NOT_BLOCK)
-		return -ECHILD;
-
 	acl = jffs2_get_acl(inode, ACL_TYPE_ACCESS);
 	if (IS_ERR(acl))
 		return PTR_ERR(acl);

fs/jfs/acl.c

@@ -118,9 +118,6 @@ int jfs_check_acl(struct inode *inode, int mask)
 {
 	struct posix_acl *acl;
 
-	if (mask & MAY_NOT_BLOCK)
-		return -ECHILD;
-
 	acl = jfs_get_acl(inode, ACL_TYPE_ACCESS);
 	if (IS_ERR(acl))
 		return PTR_ERR(acl);

fs/namei.c

@@ -32,6 +32,7 @@
 #include <linux/fcntl.h>
 #include <linux/device_cgroup.h>
 #include <linux/fs_struct.h>
+#include <linux/posix_acl.h>
 #include <asm/uaccess.h>
 
 #include "internal.h"
@@ -173,12 +174,58 @@ void putname(const char *name)
 EXPORT_SYMBOL(putname);
 #endif
 
+static int check_acl(struct inode *inode, int mask)
+{
+	struct posix_acl *acl;
+
+	/*
+	 * Under RCU walk, we cannot even do a "get_cached_acl()",
+	 * because that involves locking and getting a refcount on
+	 * a cached ACL.
+	 *
+	 * So the only case we handle during RCU walking is the
+	 * case of a cached "no ACL at all", which needs no locks
+	 * or refcounts.
+	 */
+	if (mask & MAY_NOT_BLOCK) {
+	        if (negative_cached_acl(inode, ACL_TYPE_ACCESS))
+	                return -EAGAIN;
+	        return -ECHILD;
+	}
+
+	acl = get_cached_acl(inode, ACL_TYPE_ACCESS);
+
+	/*
+	 * A filesystem can force a ACL callback by just never
+	 * filling the ACL cache. But normally you'd fill the
+	 * cache either at inode instantiation time, or on the
+	 * first ->check_acl call.
+	 *
+	 * If the filesystem doesn't have a check_acl() function
+	 * at all, we'll just create the negative cache entry.
+	 */
+	if (acl == ACL_NOT_CACHED) {
+	        if (inode->i_op->check_acl)
+	                return inode->i_op->check_acl(inode, mask);
+
+	        set_cached_acl(inode, ACL_TYPE_ACCESS, NULL);
+	        return -EAGAIN;
+	}
+
+	if (acl) {
+	        int error = posix_acl_permission(inode, acl, mask);
+	        posix_acl_release(acl);
+	        return error;
+	}
+
+	return -EAGAIN;
+}
+
 /*
  * This does basic POSIX ACL permission checking
  */
 static int acl_permission_check(struct inode *inode, int mask)
 {
-	int (*check_acl)(struct inode *inode, int mask);
 	unsigned int mode = inode->i_mode;
 
 	mask &= MAY_READ | MAY_WRITE | MAY_EXEC | MAY_NOT_BLOCK;
@@ -189,8 +236,7 @@ static int acl_permission_check(struct inode *inode, int mask)
 	if (current_fsuid() == inode->i_uid)
 		mode >>= 6;
 	else {
-		check_acl = inode->i_op->check_acl;
-		if (IS_POSIXACL(inode) && (mode & S_IRWXG) && check_acl) {
+		if (IS_POSIXACL(inode) && (mode & S_IRWXG)) {
 			int error = check_acl(inode, mask);
 			if (error != -EAGAIN)
 				return error;

fs/ocfs2/acl.c

@@ -297,9 +297,6 @@ int ocfs2_check_acl(struct inode *inode, int mask)
 	struct posix_acl *acl;
 	int ret = -EAGAIN;
 
-	if (mask & MAY_NOT_BLOCK)
-		return -ECHILD;
-
 	osb = OCFS2_SB(inode->i_sb);
 	if (!(osb->s_mount_opt & OCFS2_MOUNT_POSIX_ACL))
 		return ret;

fs/xfs/linux-2.6/xfs_acl.c

@@ -231,16 +231,12 @@ xfs_check_acl(struct inode *inode, int mask)
 	/*
 	 * If there is no attribute fork no ACL exists on this inode and
 	 * we can skip the whole exercise.
+	 *
+	 * FIXME! Fill the cache! Locking?
 	 */
 	if (!XFS_IFORK_Q(ip))
 		return -EAGAIN;
 
-	if (mask & MAY_NOT_BLOCK) {
-		if (!negative_cached_acl(inode, ACL_TYPE_ACCESS))
-			return -ECHILD;
-		return -EAGAIN;
-	}
-
 	acl = xfs_get_acl(inode, ACL_TYPE_ACCESS);
 	if (IS_ERR(acl))
 		return PTR_ERR(acl);