linux/fs/file_table.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 *  linux/fs/file_table.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *  Copyright (C) 1997 David S. Miller ([email protected])
 */

#include <linux/string.h>
#include <linux/slab.h>
#include <linux/file.h>
#include <linux/fdtable.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/filelock.h>
#include <linux/security.h>
#include <linux/cred.h>
#include <linux/eventpoll.h>
#include <linux/rcupdate.h>
#include <linux/mount.h>
#include <linux/capability.h>
#include <linux/cdev.h>
#include <linux/fsnotify.h>
#include <linux/sysctl.h>
#include <linux/percpu_counter.h>
#include <linux/percpu.h>
#include <linux/task_work.h>
#include <linux/swap.h>
#include <linux/kmemleak.h>

#include <linux/atomic.h>

#include "internal.h"

/* sysctl tunables... */
static struct files_stat_struct files_stat = …;

/* SLAB cache for file structures */
static struct kmem_cache *filp_cachep __ro_after_init;

static struct percpu_counter nr_files __cacheline_aligned_in_smp;

/* Container for backing file with optional user path */
struct backing_file { … };

static inline struct backing_file *backing_file(struct file *f)
{ … }

struct path *backing_file_user_path(struct file *f)
{ … }
EXPORT_SYMBOL_GPL(…);

static inline void file_free(struct file *f)
{ … }

/*
 * Return the total number of open files in the system
 */
static long get_nr_files(void)
{ … }

/*
 * Return the maximum number of open files in the system
 */
unsigned long get_max_files(void)
{ … }
EXPORT_SYMBOL_GPL(…);

#if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)

/*
 * Handle nr_files sysctl
 */
static int proc_nr_files(const struct ctl_table *table, int write, void *buffer,
			 size_t *lenp, loff_t *ppos)
{ … }

static struct ctl_table fs_stat_sysctls[] = …;

static int __init init_fs_stat_sysctls(void)
{ … }
fs_initcall(init_fs_stat_sysctls);
#endif

static int init_file(struct file *f, int flags, const struct cred *cred)
{ … }

/* Find an unused file structure and return a pointer to it.
 * Returns an error pointer if some error happend e.g. we over file
 * structures limit, run out of memory or operation is not permitted.
 *
 * Be very careful using this.  You are responsible for
 * getting write access to any mount that you might assign
 * to this filp, if it is opened for write.  If this is not
 * done, you will imbalance int the mount's writer count
 * and a warning at __fput() time.
 */
struct file *alloc_empty_file(int flags, const struct cred *cred)
{ … }

/*
 * Variant of alloc_empty_file() that doesn't check and modify nr_files.
 *
 * This is only for kernel internal use, and the allocate file must not be
 * installed into file tables or such.
 */
struct file *alloc_empty_file_noaccount(int flags, const struct cred *cred)
{ … }

/*
 * Variant of alloc_empty_file() that allocates a backing_file container
 * and doesn't check and modify nr_files.
 *
 * This is only for kernel internal use, and the allocate file must not be
 * installed into file tables or such.
 */
struct file *alloc_empty_backing_file(int flags, const struct cred *cred)
{ … }

/**
 * file_init_path - initialize a 'struct file' based on path
 *
 * @file: the file to set up
 * @path: the (dentry, vfsmount) pair for the new file
 * @fop: the 'struct file_operations' for the new file
 */
static void file_init_path(struct file *file, const struct path *path,
			   const struct file_operations *fop)
{ … }

/**
 * alloc_file - allocate and initialize a 'struct file'
 *
 * @path: the (dentry, vfsmount) pair for the new file
 * @flags: O_... flags with which the new file will be opened
 * @fop: the 'struct file_operations' for the new file
 */
static struct file *alloc_file(const struct path *path, int flags,
		const struct file_operations *fop)
{ … }

static inline int alloc_path_pseudo(const char *name, struct inode *inode,
				    struct vfsmount *mnt, struct path *path)
{ … }

struct file *alloc_file_pseudo(struct inode *inode, struct vfsmount *mnt,
			       const char *name, int flags,
			       const struct file_operations *fops)
{ … }
EXPORT_SYMBOL(…);

struct file *alloc_file_pseudo_noaccount(struct inode *inode,
					 struct vfsmount *mnt, const char *name,
					 int flags,
					 const struct file_operations *fops)
{ … }
EXPORT_SYMBOL_GPL(…);

struct file *alloc_file_clone(struct file *base, int flags,
				const struct file_operations *fops)
{ … }

/* the real guts of fput() - releasing the last reference to file
 */
static void __fput(struct file *file)
{ … }

static LLIST_HEAD(delayed_fput_list);
static void delayed_fput(struct work_struct *unused)
{ … }

static void ____fput(struct callback_head *work)
{ … }

/*
 * If kernel thread really needs to have the final fput() it has done
 * to complete, call this.  The only user right now is the boot - we
 * *do* need to make sure our writes to binaries on initramfs has
 * not left us with opened struct file waiting for __fput() - execve()
 * won't work without that.  Please, don't add more callers without
 * very good reasons; in particular, never call that with locks
 * held and never call that from a thread that might need to do
 * some work on any kind of umount.
 */
void flush_delayed_fput(void)
{ … }
EXPORT_SYMBOL_GPL(…);

static DECLARE_DELAYED_WORK(delayed_fput_work, delayed_fput);

void fput(struct file *file)
{ … }

/*
 * synchronous analog of fput(); for kernel threads that might be needed
 * in some umount() (and thus can't use flush_delayed_fput() without
 * risking deadlocks), need to wait for completion of __fput() and know
 * for this specific struct file it won't involve anything that would
 * need them.  Use only if you really need it - at the very least,
 * don't blindly convert fput() by kernel thread to that.
 */
void __fput_sync(struct file *file)
{ … }

EXPORT_SYMBOL(…);
EXPORT_SYMBOL(…);

void __init files_init(void)
{ … }

/*
 * One file with associated inode and dcache is very roughly 1K. Per default
 * do not use more than 10% of our memory for files.
 */
void __init files_maxfiles_init(void)
{ … }