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![Eric W. Biederman](/assets/img/avatar_default.png)
The problem. When implementing a network namespace I need to be able to have multiple network devices with the same name. Currently this is a problem for /sys/class/net/*, /sys/devices/virtual/net/*, and potentially a few other directories of the form /sys/ ... /net/*. What this patch does is to add an additional tag field to the sysfs dirent structure. For directories that should show different contents depending on the context such as /sys/class/net/, and /sys/devices/virtual/net/ this tag field is used to specify the context in which those directories should be visible. Effectively this is the same as creating multiple distinct directories with the same name but internally to sysfs the result is nicer. I am calling the concept of a single directory that looks like multiple directories all at the same path in the filesystem tagged directories. For the networking namespace the set of directories whose contents I need to filter with tags can depend on the presence or absence of hotplug hardware or which modules are currently loaded. Which means I need a simple race free way to setup those directories as tagged. To achieve a reace free design all tagged directories are created and managed by sysfs itself. Users of this interface: - define a type in the sysfs_tag_type enumeration. - call sysfs_register_ns_types with the type and it's operations - sysfs_exit_ns when an individual tag is no longer valid - Implement mount_ns() which returns the ns of the calling process so we can attach it to a sysfs superblock. - Implement ktype.namespace() which returns the ns of a syfs kobject. Everything else is left up to sysfs and the driver layer. For the network namespace mount_ns and namespace() are essentially one line functions, and look to remain that. Tags are currently represented a const void * pointers as that is both generic, prevides enough information for equality comparisons, and is trivial to create for current users, as it is just the existing namespace pointer. The work needed in sysfs is more extensive. At each directory or symlink creating I need to check if the directory it is being created in is a tagged directory and if so generate the appropriate tag to place on the sysfs_dirent. Likewise at each symlink or directory removal I need to check if the sysfs directory it is being removed from is a tagged directory and if so figure out which tag goes along with the name I am deleting. Currently only directories which hold kobjects, and symlinks are supported. There is not enough information in the current file attribute interfaces to give us anything to discriminate on which makes it useless, and there are no potential users which makes it an uninteresting problem to solve. Signed-off-by: Eric W. Biederman <ebiederm@xmission.com> Signed-off-by: Benjamin Thery <benjamin.thery@bull.net> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
154 lines
3.8 KiB
C
154 lines
3.8 KiB
C
/*
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* fs/sysfs/group.c - Operations for adding/removing multiple files at once.
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*
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* Copyright (c) 2003 Patrick Mochel
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* Copyright (c) 2003 Open Source Development Lab
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*
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* This file is released undert the GPL v2.
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*
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*/
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#include <linux/kobject.h>
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#include <linux/module.h>
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#include <linux/dcache.h>
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#include <linux/namei.h>
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#include <linux/err.h>
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#include "sysfs.h"
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static void remove_files(struct sysfs_dirent *dir_sd, struct kobject *kobj,
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const struct attribute_group *grp)
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{
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struct attribute *const* attr;
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int i;
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for (i = 0, attr = grp->attrs; *attr; i++, attr++)
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sysfs_hash_and_remove(dir_sd, NULL, (*attr)->name);
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}
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static int create_files(struct sysfs_dirent *dir_sd, struct kobject *kobj,
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const struct attribute_group *grp, int update)
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{
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struct attribute *const* attr;
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int error = 0, i;
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for (i = 0, attr = grp->attrs; *attr && !error; i++, attr++) {
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mode_t mode = 0;
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/* in update mode, we're changing the permissions or
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* visibility. Do this by first removing then
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* re-adding (if required) the file */
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if (update)
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sysfs_hash_and_remove(dir_sd, NULL, (*attr)->name);
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if (grp->is_visible) {
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mode = grp->is_visible(kobj, *attr, i);
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if (!mode)
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continue;
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}
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error = sysfs_add_file_mode(dir_sd, *attr, SYSFS_KOBJ_ATTR,
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(*attr)->mode | mode);
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if (unlikely(error))
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break;
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}
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if (error)
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remove_files(dir_sd, kobj, grp);
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return error;
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}
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static int internal_create_group(struct kobject *kobj, int update,
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const struct attribute_group *grp)
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{
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struct sysfs_dirent *sd;
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int error;
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BUG_ON(!kobj || (!update && !kobj->sd));
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/* Updates may happen before the object has been instantiated */
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if (unlikely(update && !kobj->sd))
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return -EINVAL;
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if (grp->name) {
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error = sysfs_create_subdir(kobj, grp->name, &sd);
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if (error)
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return error;
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} else
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sd = kobj->sd;
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sysfs_get(sd);
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error = create_files(sd, kobj, grp, update);
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if (error) {
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if (grp->name)
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sysfs_remove_subdir(sd);
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}
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sysfs_put(sd);
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return error;
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}
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/**
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* sysfs_create_group - given a directory kobject, create an attribute group
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* @kobj: The kobject to create the group on
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* @grp: The attribute group to create
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*
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* This function creates a group for the first time. It will explicitly
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* warn and error if any of the attribute files being created already exist.
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*
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* Returns 0 on success or error.
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*/
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int sysfs_create_group(struct kobject *kobj,
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const struct attribute_group *grp)
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{
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return internal_create_group(kobj, 0, grp);
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}
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/**
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* sysfs_update_group - given a directory kobject, create an attribute group
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* @kobj: The kobject to create the group on
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* @grp: The attribute group to create
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*
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* This function updates an attribute group. Unlike
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* sysfs_create_group(), it will explicitly not warn or error if any
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* of the attribute files being created already exist. Furthermore,
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* if the visibility of the files has changed through the is_visible()
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* callback, it will update the permissions and add or remove the
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* relevant files.
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*
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* The primary use for this function is to call it after making a change
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* that affects group visibility.
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*
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* Returns 0 on success or error.
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*/
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int sysfs_update_group(struct kobject *kobj,
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const struct attribute_group *grp)
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{
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return internal_create_group(kobj, 1, grp);
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}
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void sysfs_remove_group(struct kobject * kobj,
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const struct attribute_group * grp)
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{
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struct sysfs_dirent *dir_sd = kobj->sd;
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struct sysfs_dirent *sd;
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if (grp->name) {
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sd = sysfs_get_dirent(dir_sd, NULL, grp->name);
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if (!sd) {
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WARN(!sd, KERN_WARNING "sysfs group %p not found for "
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"kobject '%s'\n", grp, kobject_name(kobj));
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return;
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}
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} else
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sd = sysfs_get(dir_sd);
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remove_files(sd, kobj, grp);
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if (grp->name)
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sysfs_remove_subdir(sd);
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sysfs_put(sd);
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}
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EXPORT_SYMBOL_GPL(sysfs_create_group);
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EXPORT_SYMBOL_GPL(sysfs_update_group);
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EXPORT_SYMBOL_GPL(sysfs_remove_group);
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