path: root/fs/super.c

/*
 *  linux/fs/super.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *
 *  super.c contains code to handle: - mount structures
 *                                   - super-block tables
 *                                   - filesystem drivers list
 *                                   - mount system call
 *                                   - umount system call
 *                                   - ustat system call
 *
 * GK 2/5/95  -  Changed to support mounting the root fs via NFS
 *
 *  Added kerneld support: Jacques Gelinas and Bjorn Ekwall
 *  Added change_root: Werner Almesberger & Hans Lermen, Feb '96
 *  Added options to /proc/mounts:
 *    Torbjörn Lindh (torbjorn.lindh@gopta.se), April 14, 1996.
 *  Added devfs support: Richard Gooch <rgooch@atnf.csiro.au>, 13-JAN-1998
 *  Heavily rewritten for 'one fs - one tree' dcache architecture. AV, Mar 2000
 */

#include <linux/module.h>
#include <linux/slab.h>
#include <linux/acct.h>
#include <linux/blkdev.h>
#include <linux/mount.h>
#include <linux/security.h>
#include <linux/writeback.h>		/* for the emergency remount stuff */
#include <linux/idr.h>
#include <linux/mutex.h>
#include <linux/backing-dev.h>
#include <linux/rculist_bl.h>
#include <linux/cleancache.h>
#include "internal.h"


LIST_HEAD(super_blocks);
DEFINE_SPINLOCK(sb_lock);

/*
 * One thing we have to be careful of with a per-sb shrinker is that we don't
 * drop the last active reference to the superblock from within the shrinker.
 * If that happens we could trigger unregistering the shrinker from within the
 * shrinker path and that leads to deadlock on the shrinker_rwsem. Hence we
 * take a passive reference to the superblock to avoid this from occurring.
 */
static int prune_super(struct shrinker *shrink, struct shrink_control *sc)
{
	struct super_block *sb;
	int	fs_objects = 0;
	int	total_objects;

	sb = container_of(shrink, struct super_block, s_shrink);

	/*
	 * Deadlock avoidance.  We may hold various FS locks, and we don't want
	 * to recurse into the FS that called us in clear_inode() and friends..
	 */
	if (sc->nr_to_scan && !(sc->gfp_mask & __GFP_FS))
		return -1;

	if (!grab_super_passive(sb))
		return -1;

	if (sb->s_op && sb->s_op->nr_cached_objects)
		fs_objects = sb->s_op->nr_cached_objects(sb);

	total_objects = sb->s_nr_dentry_unused +
			sb->s_nr_inodes_unused + fs_objects + 1;

	if (sc->nr_to_scan) {
		int	dentries;
		int	inodes;

		/* proportion the scan between the caches */
		dentries = (sc->nr_to_scan * sb->s_nr_dentry_unused) /
							total_objects;
		inodes = (sc->nr_to_scan * sb->s_nr_inodes_unused) /
							total_objects;
		if (fs_objects)
			fs_objects = (sc->nr_to_scan * fs_objects) /
							total_objects;
		/*
		 * prune the dcache first as the icache is pinned by it, then
		 * prune the icache, followed by the filesystem specific caches
		 */
		prune_dcache_sb(sb, dentries);
		prune_icache_sb(sb, inodes);

		if (fs_objects && sb->s_op->free_cached_objects) {
			sb->s_op->free_cached_objects(sb, fs_objects);
			fs_objects = sb->s_op->nr_cached_objects(sb);
		}
		total_objects = sb->s_nr_dentry_unused +
				sb->s_nr_inodes_unused + fs_objects;
	}

	total_objects = (total_objects / 100) * sysctl_vfs_cache_pressure;
	drop_super(sb);
	return total_objects;
}

/**
 *	alloc_super	-	create new superblock
 *	@type:	filesystem type superblock should belong to
 *
 *	Allocates and initializes a new &struct super_block.  alloc_super()
 *	returns a pointer new superblock or %NULL if allocation had failed.
 */
static struct super_block *alloc_super(struct file_system_type *type)
{
	struct super_block *s = kzalloc(sizeof(struct super_block),  GFP_USER);
	static const struct super_operations default_op;

	if (s) {
		if (security_sb_alloc(