From be867b194a3ae3c680c29521287ae49b4d44d420 Mon Sep 17 00:00:00 2001 From: "Serge E. Hallyn" Date: Mon, 3 May 2010 16:23:15 -0500 Subject: [PATCH] sysfs: Comment sysfs directory tagging logic Add some in-line comments to explain the new infrastructure, which was introduced to support sysfs directory tagging with namespaces. I think an overall description someplace might be good too, but it didn't really seem to fit into Documentation/filesystems/sysfs.txt, which appears more geared toward users, rather than maintainers, of sysfs. (Tejun, please let me know if I can make anything clearer or failed altogether to comment something that should be commented.) Signed-off-by: Serge E. Hallyn Cc: Eric W. Biederman Cc: Tejun Heo Signed-off-by: Greg Kroah-Hartman --- fs/sysfs/dir.c | 8 ++++++++ fs/sysfs/sysfs.h | 13 ++++++++++++- include/linux/kobject.h | 11 +++++++++++ include/linux/sysfs.h | 1 + lib/kobject.c | 11 +++++++++++ 5 files changed, 43 insertions(+), 1 deletion(-) diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c index a63eb4ba7867..7e54bac8c4b0 100644 --- a/fs/sysfs/dir.c +++ b/fs/sysfs/dir.c @@ -614,6 +614,14 @@ int sysfs_create_subdir(struct kobject *kobj, const char *name, KOBJ_NS_TYPE_NONE, NULL, name, p_sd); } +/** + * sysfs_read_ns_type: return associated ns_type + * @kobj: the kobject being queried + * + * Each kobject can be tagged with exactly one namespace type + * (i.e. network or user). Return the ns_type associated with + * this object if any + */ static enum kobj_ns_type sysfs_read_ns_type(struct kobject *kobj) { const struct kobj_ns_type_operations *ops; diff --git a/fs/sysfs/sysfs.h b/fs/sysfs/sysfs.h index 93847d54c2e3..6a13105b5594 100644 --- a/fs/sysfs/sysfs.h +++ b/fs/sysfs/sysfs.h @@ -58,7 +58,7 @@ struct sysfs_dirent { struct sysfs_dirent *s_sibling; const char *s_name; - const void *s_ns; + const void *s_ns; /* namespace tag */ union { struct sysfs_elem_dir s_dir; struct sysfs_elem_symlink s_symlink; @@ -82,6 +82,7 @@ struct sysfs_dirent { #define SYSFS_COPY_NAME (SYSFS_DIR | SYSFS_KOBJ_LINK) #define SYSFS_ACTIVE_REF (SYSFS_KOBJ_ATTR | SYSFS_KOBJ_BIN_ATTR) +/* identify any namespace tag on sysfs_dirents */ #define SYSFS_NS_TYPE_MASK 0xff00 #define SYSFS_NS_TYPE_SHIFT 8 @@ -93,6 +94,10 @@ static inline unsigned int sysfs_type(struct sysfs_dirent *sd) return sd->s_flags & SYSFS_TYPE_MASK; } +/* + * Return any namespace tags on this dirent. + * enum kobj_ns_type is defined in linux/kobject.h + */ static inline enum kobj_ns_type sysfs_ns_type(struct sysfs_dirent *sd) { return (sd->s_flags & SYSFS_NS_TYPE_MASK) >> SYSFS_NS_TYPE_SHIFT; @@ -123,6 +128,12 @@ struct sysfs_addrm_cxt { /* * mount.c */ + +/* + * Each sb is associated with a set of namespace tags (i.e. + * the network namespace of the task which mounted this sysfs + * instance). + */ struct sysfs_super_info { const void *ns[KOBJ_NS_TYPES]; }; diff --git a/include/linux/kobject.h b/include/linux/kobject.h index d9456f69904f..b60d2dfe4e69 100644 --- a/include/linux/kobject.h +++ b/include/linux/kobject.h @@ -136,12 +136,23 @@ struct kobj_attribute { extern const struct sysfs_ops kobj_sysfs_ops; +/* + * Namespace types which are used to tag kobjects and sysfs entries. + * Network namespace will likely be the first. + */ enum kobj_ns_type { KOBJ_NS_TYPE_NONE = 0, KOBJ_NS_TYPES }; struct sock; + +/* + * Callbacks so sysfs can determine namespaces + * @current_ns: return calling task's namespace + * @netlink_ns: return namespace to which a sock belongs (right?) + * @initial_ns: return the initial namespace (i.e. init_net_ns) + */ struct kobj_ns_type_operations { enum kobj_ns_type type; const void *(*current_ns)(void); diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h index 976c4664b216..47f1c95b5298 100644 --- a/include/linux/sysfs.h +++ b/include/linux/sysfs.h @@ -178,6 +178,7 @@ struct sysfs_dirent *sysfs_get(struct sysfs_dirent *sd); void sysfs_put(struct sysfs_dirent *sd); void sysfs_printk_last_file(void); +/* Called to clear a ns tag when it is no longer valid */ void sysfs_exit_ns(enum kobj_ns_type type, const void *tag); int __must_check sysfs_init(void); diff --git a/lib/kobject.c b/lib/kobject.c index b2c6d1f56e65..f07c57252e82 100644 --- a/lib/kobject.c +++ b/lib/kobject.c @@ -948,6 +948,17 @@ const void *kobj_ns_initial(enum kobj_ns_type type) return ns; } +/* + * kobj_ns_exit - invalidate a namespace tag + * + * @type: the namespace type (i.e. KOBJ_NS_TYPE_NET) + * @ns: the actual namespace being invalidated + * + * This is called when a tag is no longer valid. For instance, + * when a network namespace exits, it uses this helper to + * make sure no sb's sysfs_info points to the now-invalidated + * netns. + */ void kobj_ns_exit(enum kobj_ns_type type, const void *ns) { sysfs_exit_ns(type, ns);