linux/fs/kernfs/mount.c
Linus Torvalds 7f427d3a60 Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs
Pull parallel filesystem directory handling update from Al Viro.

This is the main parallel directory work by Al that makes the vfs layer
able to do lookup and readdir in parallel within a single directory.
That's a big change, since this used to be all protected by the
directory inode mutex.

The inode mutex is replaced by an rwsem, and serialization of lookups of
a single name is done by a "in-progress" dentry marker.

The series begins with xattr cleanups, and then ends with switching
filesystems over to actually doing the readdir in parallel (switching to
the "iterate_shared()" that only takes the read lock).

A more detailed explanation of the process from Al Viro:
 "The xattr work starts with some acl fixes, then switches ->getxattr to
  passing inode and dentry separately.  This is the point where the
  things start to get tricky - that got merged into the very beginning
  of the -rc3-based #work.lookups, to allow untangling the
  security_d_instantiate() mess.  The xattr work itself proceeds to
  switch a lot of filesystems to generic_...xattr(); no complications
  there.

  After that initial xattr work, the series then does the following:

   - untangle security_d_instantiate()

   - convert a bunch of open-coded lookup_one_len_unlocked() to calls of
     that thing; one such place (in overlayfs) actually yields a trivial
     conflict with overlayfs fixes later in the cycle - overlayfs ended
     up switching to a variant of lookup_one_len_unlocked() sans the
     permission checks.  I would've dropped that commit (it gets
     overridden on merge from #ovl-fixes in #for-next; proper resolution
     is to use the variant in mainline fs/overlayfs/super.c), but I
     didn't want to rebase the damn thing - it was fairly late in the
     cycle...

   - some filesystems had managed to depend on lookup/lookup exclusion
     for *fs-internal* data structures in a way that would break if we
     relaxed the VFS exclusion.  Fixing hadn't been hard, fortunately.

   - core of that series - parallel lookup machinery, replacing
     ->i_mutex with rwsem, making lookup_slow() take it only shared.  At
     that point lookups happen in parallel; lookups on the same name
     wait for the in-progress one to be done with that dentry.

     Surprisingly little code, at that - almost all of it is in
     fs/dcache.c, with fs/namei.c changes limited to lookup_slow() -
     making it use the new primitive and actually switching to locking
     shared.

   - parallel readdir stuff - first of all, we provide the exclusion on
     per-struct file basis, same as we do for read() vs lseek() for
     regular files.  That takes care of most of the needed exclusion in
     readdir/readdir; however, these guys are trickier than lookups, so
     I went for switching them one-by-one.  To do that, a new method
     '->iterate_shared()' is added and filesystems are switched to it
     as they are either confirmed to be OK with shared lock on directory
     or fixed to be OK with that.  I hope to kill the original method
     come next cycle (almost all in-tree filesystems are switched
     already), but it's still not quite finished.

   - several filesystems get switched to parallel readdir.  The
     interesting part here is dealing with dcache preseeding by readdir;
     that needs minor adjustment to be safe with directory locked only
     shared.

     Most of the filesystems doing that got switched to in those
     commits.  Important exception: NFS.  Turns out that NFS folks, with
     their, er, insistence on VFS getting the fuck out of the way of the
     Smart Filesystem Code That Knows How And What To Lock(tm) have
     grown the locking of their own.  They had their own homegrown
     rwsem, with lookup/readdir/atomic_open being *writers* (sillyunlink
     is the reader there).  Of course, with VFS getting the fuck out of
     the way, as requested, the actual smarts of the smart filesystem
     code etc. had become exposed...

   - do_last/lookup_open/atomic_open cleanups.  As the result, open()
     without O_CREAT locks the directory only shared.  Including the
     ->atomic_open() case.  Backmerge from #for-linus in the middle of
     that - atomic_open() fix got brought in.

   - then comes NFS switch to saner (VFS-based ;-) locking, killing the
     homegrown "lookup and readdir are writers" kinda-sorta rwsem.  All
     exclusion for sillyunlink/lookup is done by the parallel lookups
     mechanism.  Exclusion between sillyunlink and rmdir is a real rwsem
     now - rmdir being the writer.

     Result: NFS lookups/readdirs/O_CREAT-less opens happen in parallel
     now.

   - the rest of the series consists of switching a lot of filesystems
     to parallel readdir; in a lot of cases ->llseek() gets simplified
     as well.  One backmerge in there (again, #for-linus - rockridge
     fix)"

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: (74 commits)
  ext4: switch to ->iterate_shared()
  hfs: switch to ->iterate_shared()
  hfsplus: switch to ->iterate_shared()
  hostfs: switch to ->iterate_shared()
  hpfs: switch to ->iterate_shared()
  hpfs: handle allocation failures in hpfs_add_pos()
  gfs2: switch to ->iterate_shared()
  f2fs: switch to ->iterate_shared()
  afs: switch to ->iterate_shared()
  befs: switch to ->iterate_shared()
  befs: constify stuff a bit
  isofs: switch to ->iterate_shared()
  get_acorn_filename(): deobfuscate a bit
  btrfs: switch to ->iterate_shared()
  logfs: no need to lock directory in lseek
  switch ecryptfs to ->iterate_shared
  9p: switch to ->iterate_shared()
  fat: switch to ->iterate_shared()
  romfs, squashfs: switch to ->iterate_shared()
  more trivial ->iterate_shared conversions
  ...
2016-05-17 11:01:31 -07:00

333 lines
8.4 KiB
C

/*
* fs/kernfs/mount.c - kernfs mount implementation
*
* Copyright (c) 2001-3 Patrick Mochel
* Copyright (c) 2007 SUSE Linux Products GmbH
* Copyright (c) 2007, 2013 Tejun Heo <tj@kernel.org>
*
* This file is released under the GPLv2.
*/
#include <linux/fs.h>
#include <linux/mount.h>
#include <linux/init.h>
#include <linux/magic.h>
#include <linux/slab.h>
#include <linux/pagemap.h>
#include <linux/namei.h>
#include <linux/seq_file.h>
#include "kernfs-internal.h"
struct kmem_cache *kernfs_node_cache;
static int kernfs_sop_remount_fs(struct super_block *sb, int *flags, char *data)
{
struct kernfs_root *root = kernfs_info(sb)->root;
struct kernfs_syscall_ops *scops = root->syscall_ops;
if (scops && scops->remount_fs)
return scops->remount_fs(root, flags, data);
return 0;
}
static int kernfs_sop_show_options(struct seq_file *sf, struct dentry *dentry)
{
struct kernfs_root *root = kernfs_root(dentry->d_fsdata);
struct kernfs_syscall_ops *scops = root->syscall_ops;
if (scops && scops->show_options)
return scops->show_options(sf, root);
return 0;
}
static int kernfs_sop_show_path(struct seq_file *sf, struct dentry *dentry)
{
struct kernfs_node *node = dentry->d_fsdata;
struct kernfs_root *root = kernfs_root(node);
struct kernfs_syscall_ops *scops = root->syscall_ops;
if (scops && scops->show_path)
return scops->show_path(sf, node, root);
seq_dentry(sf, dentry, " \t\n\\");
return 0;
}
const struct super_operations kernfs_sops = {
.statfs = simple_statfs,
.drop_inode = generic_delete_inode,
.evict_inode = kernfs_evict_inode,
.remount_fs = kernfs_sop_remount_fs,
.show_options = kernfs_sop_show_options,
.show_path = kernfs_sop_show_path,
};
/**
* kernfs_root_from_sb - determine kernfs_root associated with a super_block
* @sb: the super_block in question
*
* Return the kernfs_root associated with @sb. If @sb is not a kernfs one,
* %NULL is returned.
*/
struct kernfs_root *kernfs_root_from_sb(struct super_block *sb)
{
if (sb->s_op == &kernfs_sops)
return kernfs_info(sb)->root;
return NULL;
}
/*
* find the next ancestor in the path down to @child, where @parent was the
* ancestor whose descendant we want to find.
*
* Say the path is /a/b/c/d. @child is d, @parent is NULL. We return the root
* node. If @parent is b, then we return the node for c.
* Passing in d as @parent is not ok.
*/
static struct kernfs_node *find_next_ancestor(struct kernfs_node *child,
struct kernfs_node *parent)
{
if (child == parent) {
pr_crit_once("BUG in find_next_ancestor: called with parent == child");
return NULL;
}
while (child->parent != parent) {
if (!child->parent)
return NULL;
child = child->parent;
}
return child;
}
/**
* kernfs_node_dentry - get a dentry for the given kernfs_node
* @kn: kernfs_node for which a dentry is needed
* @sb: the kernfs super_block
*/
struct dentry *kernfs_node_dentry(struct kernfs_node *kn,
struct super_block *sb)
{
struct dentry *dentry;
struct kernfs_node *knparent = NULL;
BUG_ON(sb->s_op != &kernfs_sops);
dentry = dget(sb->s_root);
/* Check if this is the root kernfs_node */
if (!kn->parent)
return dentry;
knparent = find_next_ancestor(kn, NULL);
if (WARN_ON(!knparent))
return ERR_PTR(-EINVAL);
do {
struct dentry *dtmp;
struct kernfs_node *kntmp;
if (kn == knparent)
return dentry;
kntmp = find_next_ancestor(kn, knparent);
if (WARN_ON(!kntmp))
return ERR_PTR(-EINVAL);
dtmp = lookup_one_len_unlocked(kntmp->name, dentry,
strlen(kntmp->name));
dput(dentry);
if (IS_ERR(dtmp))
return dtmp;
knparent = kntmp;
dentry = dtmp;
} while (true);
}
static int kernfs_fill_super(struct super_block *sb, unsigned long magic)
{
struct kernfs_super_info *info = kernfs_info(sb);
struct inode *inode;
struct dentry *root;
info->sb = sb;
sb->s_blocksize = PAGE_SIZE;
sb->s_blocksize_bits = PAGE_SHIFT;
sb->s_magic = magic;
sb->s_op = &kernfs_sops;
sb->s_time_gran = 1;
/* get root inode, initialize and unlock it */
mutex_lock(&kernfs_mutex);
inode = kernfs_get_inode(sb, info->root->kn);
mutex_unlock(&kernfs_mutex);
if (!inode) {
pr_debug("kernfs: could not get root inode\n");
return -ENOMEM;
}
/* instantiate and link root dentry */
root = d_make_root(inode);
if (!root) {
pr_debug("%s: could not get root dentry!\n", __func__);
return -ENOMEM;
}
kernfs_get(info->root->kn);
root->d_fsdata = info->root->kn;
sb->s_root = root;
sb->s_d_op = &kernfs_dops;
return 0;
}
static int kernfs_test_super(struct super_block *sb, void *data)
{
struct kernfs_super_info *sb_info = kernfs_info(sb);
struct kernfs_super_info *info = data;
return sb_info->root == info->root && sb_info->ns == info->ns;
}
static int kernfs_set_super(struct super_block *sb, void *data)
{
int error;
error = set_anon_super(sb, data);
if (!error)
sb->s_fs_info = data;
return error;
}
/**
* kernfs_super_ns - determine the namespace tag of a kernfs super_block
* @sb: super_block of interest
*
* Return the namespace tag associated with kernfs super_block @sb.
*/
const void *kernfs_super_ns(struct super_block *sb)
{
struct kernfs_super_info *info = kernfs_info(sb);
return info->ns;
}
/**
* kernfs_mount_ns - kernfs mount helper
* @fs_type: file_system_type of the fs being mounted
* @flags: mount flags specified for the mount
* @root: kernfs_root of the hierarchy being mounted
* @magic: file system specific magic number
* @new_sb_created: tell the caller if we allocated a new superblock
* @ns: optional namespace tag of the mount
*
* This is to be called from each kernfs user's file_system_type->mount()
* implementation, which should pass through the specified @fs_type and
* @flags, and specify the hierarchy and namespace tag to mount via @root
* and @ns, respectively.
*
* The return value can be passed to the vfs layer verbatim.
*/
struct dentry *kernfs_mount_ns(struct file_system_type *fs_type, int flags,
struct kernfs_root *root, unsigned long magic,
bool *new_sb_created, const void *ns)
{
struct super_block *sb;
struct kernfs_super_info *info;
int error;
info = kzalloc(sizeof(*info), GFP_KERNEL);
if (!info)
return ERR_PTR(-ENOMEM);
info->root = root;
info->ns = ns;
sb = sget(fs_type, kernfs_test_super, kernfs_set_super, flags, info);
if (IS_ERR(sb) || sb->s_fs_info != info)
kfree(info);
if (IS_ERR(sb))
return ERR_CAST(sb);
if (new_sb_created)
*new_sb_created = !sb->s_root;
if (!sb->s_root) {
struct kernfs_super_info *info = kernfs_info(sb);
error = kernfs_fill_super(sb, magic);
if (error) {
deactivate_locked_super(sb);
return ERR_PTR(error);
}
sb->s_flags |= MS_ACTIVE;
mutex_lock(&kernfs_mutex);
list_add(&info->node, &root->supers);
mutex_unlock(&kernfs_mutex);
}
return dget(sb->s_root);
}
/**
* kernfs_kill_sb - kill_sb for kernfs
* @sb: super_block being killed
*
* This can be used directly for file_system_type->kill_sb(). If a kernfs
* user needs extra cleanup, it can implement its own kill_sb() and call
* this function at the end.
*/
void kernfs_kill_sb(struct super_block *sb)
{
struct kernfs_super_info *info = kernfs_info(sb);
struct kernfs_node *root_kn = sb->s_root->d_fsdata;
mutex_lock(&kernfs_mutex);
list_del(&info->node);
mutex_unlock(&kernfs_mutex);
/*
* Remove the superblock from fs_supers/s_instances
* so we can't find it, before freeing kernfs_super_info.
*/
kill_anon_super(sb);
kfree(info);
kernfs_put(root_kn);
}
/**
* kernfs_pin_sb: try to pin the superblock associated with a kernfs_root
* @kernfs_root: the kernfs_root in question
* @ns: the namespace tag
*
* Pin the superblock so the superblock won't be destroyed in subsequent
* operations. This can be used to block ->kill_sb() which may be useful
* for kernfs users which dynamically manage superblocks.
*
* Returns NULL if there's no superblock associated to this kernfs_root, or
* -EINVAL if the superblock is being freed.
*/
struct super_block *kernfs_pin_sb(struct kernfs_root *root, const void *ns)
{
struct kernfs_super_info *info;
struct super_block *sb = NULL;
mutex_lock(&kernfs_mutex);
list_for_each_entry(info, &root->supers, node) {
if (info->ns == ns) {
sb = info->sb;
if (!atomic_inc_not_zero(&info->sb->s_active))
sb = ERR_PTR(-EINVAL);
break;
}
}
mutex_unlock(&kernfs_mutex);
return sb;
}
void __init kernfs_init(void)
{
kernfs_node_cache = kmem_cache_create("kernfs_node_cache",
sizeof(struct kernfs_node),
0, SLAB_PANIC, NULL);
}