linux-kernel - [PATCH v2 2/4] kernfs: Add removed_size out param for simple_xattr

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Date:   Thu,  5 Mar 2020 13:16:30 -0800
From:   Daniel Xu <dxu@...uu.xyz>
To:     cgroups@...r.kernel.org, tj@...nel.org, lizefan@...wei.com,
        hannes@...xchg.org
Cc:     Daniel Xu <dxu@...uu.xyz>, shakeelb@...gle.com,
        linux-kernel@...r.kernel.org, gregkh@...uxfoundation.org,
        kernel-team@...com
Subject: [PATCH v2 2/4] kernfs: Add removed_size out param for simple_xattr_set

This helps set up size accounting in the next commit. Without this out
param, it's difficult to find out the removed xattr size without taking
a lock for longer and walking the xattr linked list twice.

Signed-off-by: Daniel Xu <dxu@...uu.xyz>
---
 fs/kernfs/inode.c     |  2 +-
 fs/xattr.c            | 11 ++++++++++-
 include/linux/xattr.h |  3 ++-
 mm/shmem.c            |  2 +-
 4 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/fs/kernfs/inode.c b/fs/kernfs/inode.c
index d0f7a5abd9a9..5f10ae95fbfa 100644
--- a/fs/kernfs/inode.c
+++ b/fs/kernfs/inode.c
@@ -303,7 +303,7 @@ int kernfs_xattr_set(struct kernfs_node *kn, const char *name,
 	if (!attrs)
 		return -ENOMEM;
 
-	return simple_xattr_set(&attrs->xattrs, name, value, size, flags);
+	return simple_xattr_set(&attrs->xattrs, name, value, size, flags, NULL);
 }
 
 static int kernfs_vfs_xattr_get(const struct xattr_handler *handler,
diff --git a/fs/xattr.c b/fs/xattr.c
index 0d3c9b4d1914..e13265e65871 100644
--- a/fs/xattr.c
+++ b/fs/xattr.c
@@ -860,6 +860,7 @@ int simple_xattr_get(struct simple_xattrs *xattrs, const char *name,
  * @value: value of the xattr. If %NULL, will remove the attribute.
  * @size: size of the new xattr
  * @flags: %XATTR_{CREATE|REPLACE}
+ * @removed_size: returns size of the removed xattr, -1 if none removed
  *
  * %XATTR_CREATE is set, the xattr shouldn't exist already; otherwise fails
  * with -EEXIST.  If %XATTR_REPLACE is set, the xattr should exist;
@@ -868,7 +869,8 @@ int simple_xattr_get(struct simple_xattrs *xattrs, const char *name,
  * Returns 0 on success, -errno on failure.
  */
 int simple_xattr_set(struct simple_xattrs *xattrs, const char *name,
-		     const void *value, size_t size, int flags)
+		     const void *value, size_t size, int flags,
+		     ssize_t *removed_size)
 {
 	struct simple_xattr *xattr;
 	struct simple_xattr *new_xattr = NULL;
@@ -895,8 +897,12 @@ int simple_xattr_set(struct simple_xattrs *xattrs, const char *name,
 				err = -EEXIST;
 			} else if (new_xattr) {
 				list_replace(&xattr->list, &new_xattr->list);
+				if (removed_size)
+					*removed_size = xattr->size;
 			} else {
 				list_del(&xattr->list);
+				if (removed_size)
+					*removed_size = xattr->size;
 			}
 			goto out;
 		}
@@ -908,6 +914,9 @@ int simple_xattr_set(struct simple_xattrs *xattrs, const char *name,
 		list_add(&new_xattr->list, &xattrs->head);
 		xattr = NULL;
 	}
+
+	if (removed_size)
+		*removed_size = -1;
 out:
 	spin_unlock(&xattrs->lock);
 	if (xattr) {
diff --git a/include/linux/xattr.h b/include/linux/xattr.h
index 6dad031be3c2..4cf6e11f4a3c 100644
--- a/include/linux/xattr.h
+++ b/include/linux/xattr.h
@@ -102,7 +102,8 @@ 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);
+		     const void *value, size_t size, int flags,
+		     ssize_t *removed_size);
 ssize_t simple_xattr_list(struct inode *inode, struct simple_xattrs *xattrs, char *buffer,
 			  size_t size);
 void simple_xattr_list_add(struct simple_xattrs *xattrs,
diff --git a/mm/shmem.c b/mm/shmem.c
index aad3ba74b0e9..f47347cb30f6 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -3243,7 +3243,7 @@ static int shmem_xattr_handler_set(const struct xattr_handler *handler,
 	struct shmem_inode_info *info = SHMEM_I(inode);
 
 	name = xattr_full_name(handler, name);
-	return simple_xattr_set(&info->xattrs, name, value, size, flags);
+	return simple_xattr_set(&info->xattrs, name, value, size, flags, NULL);
 }
 
 static const struct xattr_handler shmem_security_xattr_handler = {
-- 
2.21.1