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authorDaniel Xu <dxu@dxuuu.xyz>2020-03-12 13:03:16 -0700
committerTejun Heo <tj@kernel.org>2020-03-16 15:53:47 -0400
commit0c47383ba3bd10877956e41149d19644fba937d1 (patch)
treec3d3b420f3a961c2fb4ab56feed39bf129933939 /include/linux/kernfs.h
parenta46a22955bae16fc5a756af7188d3ccb25c3f797 (diff)
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kernfs: Add option to enable user xattrs
User extended attributes are useful as metadata storage for kernfs consumers like cgroups. Especially in the case of cgroups, it is useful to have a central metadata store that multiple processes/services can use to coordinate actions. A concrete example is for userspace out of memory killers. We want to let delegated cgroup subtree owners (running as non-root) to be able to say "please avoid killing this cgroup". This is especially important for desktop linux as delegated subtrees owners are less likely to run as root. This patch introduces a new flag, KERNFS_ROOT_SUPPORT_USER_XATTR, that lets kernfs consumers enable user xattr support. An initial limit of 128 entries or 128KB -- whichever is hit first -- is placed per cgroup because xattrs come from kernel memory and we don't want to let unprivileged users accidentally eat up too much kernel memory. Signed-off-by: Daniel Xu <dxu@dxuuu.xyz> Acked-by: Chris Down <chris@chrisdown.name> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Tejun Heo <tj@kernel.org>
Diffstat (limited to 'include/linux/kernfs.h')
-rw-r--r--include/linux/kernfs.h11
1 files changed, 9 insertions, 2 deletions
diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index dded2e5a9f42..89f6a4214a70 100644
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -37,8 +37,10 @@ enum kernfs_node_type {
KERNFS_LINK = 0x0004,
};
-#define KERNFS_TYPE_MASK 0x000f
-#define KERNFS_FLAG_MASK ~KERNFS_TYPE_MASK
+#define KERNFS_TYPE_MASK 0x000f
+#define KERNFS_FLAG_MASK ~KERNFS_TYPE_MASK
+#define KERNFS_MAX_USER_XATTRS 128
+#define KERNFS_USER_XATTR_SIZE_LIMIT (128 << 10)
enum kernfs_node_flag {
KERNFS_ACTIVATED = 0x0010,
@@ -78,6 +80,11 @@ enum kernfs_root_flag {
* fhandle to access nodes of the fs.
*/
KERNFS_ROOT_SUPPORT_EXPORTOP = 0x0004,
+
+ /*
+ * Support user xattrs to be written to nodes rooted at this root.
+ */
+ KERNFS_ROOT_SUPPORT_USER_XATTR = 0x0008,
};
/* type-specific structures for kernfs_node union members */