On Wed, Jun 18, 2025 at 04:37:37PM -0700, Song Liu wrote: > BPF programs, such as LSM and sched_ext, would benefit from tags on > cgroups. One common practice to apply such tags is to set xattrs on > cgroupfs files and folders. > > Introduce kfunc bpf_kernfs_read_xattr, which allows reading kernfs > xattr under RCU read lock. > > Note that, we already have bpf_get_[file|dentry]_xattr. However, these > two APIs are not ideal for reading cgroupfs xattrs, because: > > 1) These two APIs only works in sleepable contexts; > 2) There is no kfunc that matches current cgroup to cgroupfs dentry. > > Signed-off-by: Song Liu <song@xxxxxxxxxx> > --- > fs/bpf_fs_kfuncs.c | 33 +++++++++++++++++++++++++++++++++ > 1 file changed, 33 insertions(+) > > diff --git a/fs/bpf_fs_kfuncs.c b/fs/bpf_fs_kfuncs.c > index 08412532db1b..7576dbc9b340 100644 > --- a/fs/bpf_fs_kfuncs.c > +++ b/fs/bpf_fs_kfuncs.c > @@ -9,6 +9,7 @@ > #include <linux/fs.h> > #include <linux/fsnotify.h> > #include <linux/file.h> > +#include <linux/kernfs.h> > #include <linux/mm.h> > #include <linux/xattr.h> > > @@ -322,6 +323,37 @@ __bpf_kfunc int bpf_remove_dentry_xattr(struct dentry *dentry, const char *name_ > return ret; > } > > +/** > + * bpf_kernfs_read_xattr - get xattr of a kernfs node > + * @kn: kernfs_node to get xattr from > + * @name__str: name of the xattr > + * @value_p: output buffer of the xattr value > + * > + * Get xattr *name__str* of *kn* and store the output in *value_ptr*. > + * > + * For security reasons, only *name__str* with prefix "user." is allowed. > + * > + * Return: length of the xattr value on success, a negative value on error. > + */ > +__bpf_kfunc int bpf_kernfs_read_xattr(struct kernfs_node *kn, const char *name__str, > + struct bpf_dynptr *value_p) Please pass struct cgroup, then go from struct cgroup to kernfs node.
