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c1e5c95402
fanotify almost works like so: user context calls fsnotify_* function with a struct file. fsnotify takes a reference on the struct path user context goes about it's buissiness at some later point in time the fsnotify listener gets the struct path fanotify listener calls dentry_open() to create a file which userspace can deal with listener drops the reference on the struct path at some later point the listener calls close() on it's new file With the switch from struct path to struct file this presents a problem for fput() and fsnotify_close(). fsnotify_close() is called when the filp has already reached 0 and __fput() wants to do it's cleanup. The solution presented here is a bit odd. If an event is created from a struct file we take a reference on the file. We check however if the f_count was already 0 and if so we take an EXTRA reference EVEN THOUGH IT WAS ZERO. In __fput() (where we know the f_count hit 0 once) we check if the f_count is non-zero and if so we drop that 'extra' ref and return without destroying the file. Signed-off-by: Eric Paris <eparis@redhat.com>
442 lines
10 KiB
C
442 lines
10 KiB
C
/*
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* linux/fs/file_table.c
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*
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* Copyright (C) 1991, 1992 Linus Torvalds
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* Copyright (C) 1997 David S. Miller (davem@caip.rutgers.edu)
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*/
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#include <linux/string.h>
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#include <linux/slab.h>
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#include <linux/file.h>
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#include <linux/fdtable.h>
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#include <linux/init.h>
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#include <linux/module.h>
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#include <linux/fs.h>
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#include <linux/security.h>
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#include <linux/eventpoll.h>
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#include <linux/rcupdate.h>
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#include <linux/mount.h>
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#include <linux/capability.h>
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#include <linux/cdev.h>
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#include <linux/fsnotify.h>
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#include <linux/sysctl.h>
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#include <linux/percpu_counter.h>
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#include <linux/ima.h>
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#include <asm/atomic.h>
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#include "internal.h"
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/* sysctl tunables... */
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struct files_stat_struct files_stat = {
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.max_files = NR_FILE
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};
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/* public. Not pretty! */
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__cacheline_aligned_in_smp DEFINE_SPINLOCK(files_lock);
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/* SLAB cache for file structures */
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static struct kmem_cache *filp_cachep __read_mostly;
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static struct percpu_counter nr_files __cacheline_aligned_in_smp;
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static inline void file_free_rcu(struct rcu_head *head)
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{
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struct file *f = container_of(head, struct file, f_u.fu_rcuhead);
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put_cred(f->f_cred);
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kmem_cache_free(filp_cachep, f);
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}
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static inline void file_free(struct file *f)
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{
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percpu_counter_dec(&nr_files);
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file_check_state(f);
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call_rcu(&f->f_u.fu_rcuhead, file_free_rcu);
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}
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/*
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* Return the total number of open files in the system
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*/
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static int get_nr_files(void)
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{
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return percpu_counter_read_positive(&nr_files);
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}
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/*
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* Return the maximum number of open files in the system
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*/
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int get_max_files(void)
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{
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return files_stat.max_files;
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}
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EXPORT_SYMBOL_GPL(get_max_files);
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/*
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* Handle nr_files sysctl
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*/
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#if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
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int proc_nr_files(ctl_table *table, int write,
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void __user *buffer, size_t *lenp, loff_t *ppos)
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{
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files_stat.nr_files = get_nr_files();
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return proc_dointvec(table, write, buffer, lenp, ppos);
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}
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#else
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int proc_nr_files(ctl_table *table, int write,
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void __user *buffer, size_t *lenp, loff_t *ppos)
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{
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return -ENOSYS;
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}
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#endif
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/* Find an unused file structure and return a pointer to it.
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* Returns NULL, if there are no more free file structures or
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* we run out of memory.
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*
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* Be very careful using this. You are responsible for
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* getting write access to any mount that you might assign
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* to this filp, if it is opened for write. If this is not
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* done, you will imbalance int the mount's writer count
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* and a warning at __fput() time.
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*/
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struct file *get_empty_filp(void)
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{
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const struct cred *cred = current_cred();
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static int old_max;
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struct file * f;
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/*
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* Privileged users can go above max_files
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*/
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if (get_nr_files() >= files_stat.max_files && !capable(CAP_SYS_ADMIN)) {
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/*
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* percpu_counters are inaccurate. Do an expensive check before
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* we go and fail.
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*/
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if (percpu_counter_sum_positive(&nr_files) >= files_stat.max_files)
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goto over;
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}
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f = kmem_cache_zalloc(filp_cachep, GFP_KERNEL);
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if (f == NULL)
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goto fail;
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percpu_counter_inc(&nr_files);
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if (security_file_alloc(f))
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goto fail_sec;
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INIT_LIST_HEAD(&f->f_u.fu_list);
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atomic_long_set(&f->f_count, 1);
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rwlock_init(&f->f_owner.lock);
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f->f_cred = get_cred(cred);
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spin_lock_init(&f->f_lock);
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eventpoll_init_file(f);
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/* f->f_version: 0 */
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return f;
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over:
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/* Ran out of filps - report that */
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if (get_nr_files() > old_max) {
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printk(KERN_INFO "VFS: file-max limit %d reached\n",
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get_max_files());
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old_max = get_nr_files();
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}
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goto fail;
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fail_sec:
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file_free(f);
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fail:
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return NULL;
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}
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/**
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* alloc_file - allocate and initialize a 'struct file'
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* @mnt: the vfsmount on which the file will reside
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* @dentry: the dentry representing the new file
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* @mode: the mode with which the new file will be opened
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* @fop: the 'struct file_operations' for the new file
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*
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* Use this instead of get_empty_filp() to get a new
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* 'struct file'. Do so because of the same initialization
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* pitfalls reasons listed for init_file(). This is a
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* preferred interface to using init_file().
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*
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* If all the callers of init_file() are eliminated, its
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* code should be moved into this function.
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*/
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struct file *alloc_file(struct path *path, fmode_t mode,
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const struct file_operations *fop)
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{
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struct file *file;
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file = get_empty_filp();
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if (!file)
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return NULL;
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file->f_path = *path;
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file->f_mapping = path->dentry->d_inode->i_mapping;
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file->f_mode = mode;
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file->f_op = fop;
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/*
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* These mounts don't really matter in practice
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* for r/o bind mounts. They aren't userspace-
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* visible. We do this for consistency, and so
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* that we can do debugging checks at __fput()
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*/
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if ((mode & FMODE_WRITE) && !special_file(path->dentry->d_inode->i_mode)) {
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file_take_write(file);
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WARN_ON(mnt_clone_write(path->mnt));
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}
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ima_counts_get(file);
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return file;
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}
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EXPORT_SYMBOL(alloc_file);
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/**
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* drop_file_write_access - give up ability to write to a file
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* @file: the file to which we will stop writing
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*
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* This is a central place which will give up the ability
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* to write to @file, along with access to write through
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* its vfsmount.
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*/
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void drop_file_write_access(struct file *file)
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{
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struct vfsmount *mnt = file->f_path.mnt;
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struct dentry *dentry = file->f_path.dentry;
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struct inode *inode = dentry->d_inode;
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put_write_access(inode);
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if (special_file(inode->i_mode))
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return;
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if (file_check_writeable(file) != 0)
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return;
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mnt_drop_write(mnt);
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file_release_write(file);
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}
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EXPORT_SYMBOL_GPL(drop_file_write_access);
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/* the real guts of fput() - releasing the last reference to file
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*/
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static void __fput(struct file *file)
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{
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struct dentry *dentry = file->f_path.dentry;
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struct vfsmount *mnt = file->f_path.mnt;
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struct inode *inode = dentry->d_inode;
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might_sleep();
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fsnotify_close(file);
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/*
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* fsnotify_create_event may have taken one or more references on this
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* file. If it did so it left one reference for us to drop to make sure
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* its calls to fput could not prematurely destroy the file.
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*/
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if (atomic_long_read(&file->f_count))
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return fput(file);
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/*
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* The function eventpoll_release() should be the first called
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* in the file cleanup chain.
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*/
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eventpoll_release(file);
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locks_remove_flock(file);
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if (unlikely(file->f_flags & FASYNC)) {
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if (file->f_op && file->f_op->fasync)
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file->f_op->fasync(-1, file, 0);
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}
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if (file->f_op && file->f_op->release)
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file->f_op->release(inode, file);
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security_file_free(file);
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ima_file_free(file);
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if (unlikely(S_ISCHR(inode->i_mode) && inode->i_cdev != NULL))
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cdev_put(inode->i_cdev);
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fops_put(file->f_op);
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put_pid(file->f_owner.pid);
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file_kill(file);
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if (file->f_mode & FMODE_WRITE)
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drop_file_write_access(file);
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file->f_path.dentry = NULL;
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file->f_path.mnt = NULL;
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file_free(file);
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dput(dentry);
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mntput(mnt);
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}
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void fput(struct file *file)
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{
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if (atomic_long_dec_and_test(&file->f_count))
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__fput(file);
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}
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EXPORT_SYMBOL(fput);
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struct file *fget(unsigned int fd)
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{
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struct file *file;
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struct files_struct *files = current->files;
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rcu_read_lock();
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file = fcheck_files(files, fd);
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if (file) {
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if (!atomic_long_inc_not_zero(&file->f_count)) {
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/* File object ref couldn't be taken */
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rcu_read_unlock();
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return NULL;
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}
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}
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rcu_read_unlock();
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return file;
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}
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EXPORT_SYMBOL(fget);
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/*
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* Lightweight file lookup - no refcnt increment if fd table isn't shared.
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* You can use this only if it is guranteed that the current task already
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* holds a refcnt to that file. That check has to be done at fget() only
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* and a flag is returned to be passed to the corresponding fput_light().
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* There must not be a cloning between an fget_light/fput_light pair.
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*/
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struct file *fget_light(unsigned int fd, int *fput_needed)
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{
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struct file *file;
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struct files_struct *files = current->files;
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*fput_needed = 0;
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if (likely((atomic_read(&files->count) == 1))) {
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file = fcheck_files(files, fd);
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} else {
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rcu_read_lock();
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file = fcheck_files(files, fd);
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if (file) {
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if (atomic_long_inc_not_zero(&file->f_count))
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*fput_needed = 1;
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else
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/* Didn't get the reference, someone's freed */
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file = NULL;
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}
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rcu_read_unlock();
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}
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return file;
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}
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void put_filp(struct file *file)
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{
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if (atomic_long_dec_and_test(&file->f_count)) {
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security_file_free(file);
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file_kill(file);
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file_free(file);
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}
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}
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void file_move(struct file *file, struct list_head *list)
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{
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if (!list)
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return;
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file_list_lock();
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list_move(&file->f_u.fu_list, list);
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file_list_unlock();
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}
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void file_kill(struct file *file)
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{
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if (!list_empty(&file->f_u.fu_list)) {
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file_list_lock();
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list_del_init(&file->f_u.fu_list);
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file_list_unlock();
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}
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}
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int fs_may_remount_ro(struct super_block *sb)
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{
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struct file *file;
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/* Check that no files are currently opened for writing. */
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file_list_lock();
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list_for_each_entry(file, &sb->s_files, f_u.fu_list) {
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struct inode *inode = file->f_path.dentry->d_inode;
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/* File with pending delete? */
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if (inode->i_nlink == 0)
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goto too_bad;
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/* Writeable file? */
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if (S_ISREG(inode->i_mode) && (file->f_mode & FMODE_WRITE))
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goto too_bad;
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}
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file_list_unlock();
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return 1; /* Tis' cool bro. */
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too_bad:
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file_list_unlock();
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return 0;
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}
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/**
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* mark_files_ro - mark all files read-only
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* @sb: superblock in question
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*
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* All files are marked read-only. We don't care about pending
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* delete files so this should be used in 'force' mode only.
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*/
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void mark_files_ro(struct super_block *sb)
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{
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struct file *f;
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retry:
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file_list_lock();
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list_for_each_entry(f, &sb->s_files, f_u.fu_list) {
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struct vfsmount *mnt;
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if (!S_ISREG(f->f_path.dentry->d_inode->i_mode))
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continue;
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if (!file_count(f))
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continue;
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if (!(f->f_mode & FMODE_WRITE))
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continue;
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spin_lock(&f->f_lock);
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f->f_mode &= ~FMODE_WRITE;
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spin_unlock(&f->f_lock);
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if (file_check_writeable(f) != 0)
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continue;
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file_release_write(f);
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mnt = mntget(f->f_path.mnt);
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file_list_unlock();
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/*
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* This can sleep, so we can't hold
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* the file_list_lock() spinlock.
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*/
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mnt_drop_write(mnt);
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mntput(mnt);
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goto retry;
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}
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file_list_unlock();
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}
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void __init files_init(unsigned long mempages)
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{
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int n;
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filp_cachep = kmem_cache_create("filp", sizeof(struct file), 0,
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SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
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/*
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* One file with associated inode and dcache is very roughly 1K.
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* Per default don't use more than 10% of our memory for files.
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*/
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n = (mempages * (PAGE_SIZE / 1024)) / 10;
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files_stat.max_files = n;
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if (files_stat.max_files < NR_FILE)
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files_stat.max_files = NR_FILE;
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files_defer_init();
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percpu_counter_init(&nr_files, 0);
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}
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