linux/fs/notify/dnotify/dnotify.c
Amir Goldstein b9a1b97725 fsnotify: create method handle_inode_event() in fsnotify_operations
The method handle_event() grew a lot of complexity due to the design of
fanotify and merging of ignore masks.

Most backends do not care about this complex functionality, so we can hide
this complexity from them.

Introduce a method handle_inode_event() that serves those backends and
passes a single inode mark and less arguments.

This change converts all backends except fanotify and inotify to use the
simplified handle_inode_event() method.  In pricipal, inotify could have
also used the new method, but that would require passing more arguments
on the simple helper (data, data_type, cookie), so we leave it with the
handle_event() method.

Link: https://lore.kernel.org/r/20200722125849.17418-9-amir73il@gmail.com
Suggested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
2020-07-27 23:25:50 +02:00

393 lines
11 KiB
C

// SPDX-License-Identifier: GPL-2.0-or-later
/*
* Directory notifications for Linux.
*
* Copyright (C) 2000,2001,2002 Stephen Rothwell
*
* Copyright (C) 2009 Eric Paris <Red Hat Inc>
* dnotify was largly rewritten to use the new fsnotify infrastructure
*/
#include <linux/fs.h>
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/sched/signal.h>
#include <linux/dnotify.h>
#include <linux/init.h>
#include <linux/security.h>
#include <linux/spinlock.h>
#include <linux/slab.h>
#include <linux/fdtable.h>
#include <linux/fsnotify_backend.h>
int dir_notify_enable __read_mostly = 1;
static struct kmem_cache *dnotify_struct_cache __read_mostly;
static struct kmem_cache *dnotify_mark_cache __read_mostly;
static struct fsnotify_group *dnotify_group __read_mostly;
/*
* dnotify will attach one of these to each inode (i_fsnotify_marks) which
* is being watched by dnotify. If multiple userspace applications are watching
* the same directory with dnotify their information is chained in dn
*/
struct dnotify_mark {
struct fsnotify_mark fsn_mark;
struct dnotify_struct *dn;
};
/*
* When a process starts or stops watching an inode the set of events which
* dnotify cares about for that inode may change. This function runs the
* list of everything receiving dnotify events about this directory and calculates
* the set of all those events. After it updates what dnotify is interested in
* it calls the fsnotify function so it can update the set of all events relevant
* to this inode.
*/
static void dnotify_recalc_inode_mask(struct fsnotify_mark *fsn_mark)
{
__u32 new_mask = 0;
struct dnotify_struct *dn;
struct dnotify_mark *dn_mark = container_of(fsn_mark,
struct dnotify_mark,
fsn_mark);
assert_spin_locked(&fsn_mark->lock);
for (dn = dn_mark->dn; dn != NULL; dn = dn->dn_next)
new_mask |= (dn->dn_mask & ~FS_DN_MULTISHOT);
if (fsn_mark->mask == new_mask)
return;
fsn_mark->mask = new_mask;
fsnotify_recalc_mask(fsn_mark->connector);
}
/*
* Mains fsnotify call where events are delivered to dnotify.
* Find the dnotify mark on the relevant inode, run the list of dnotify structs
* on that mark and determine which of them has expressed interest in receiving
* events of this type. When found send the correct process and signal and
* destroy the dnotify struct if it was not registered to receive multiple
* events.
*/
static int dnotify_handle_event(struct fsnotify_mark *inode_mark, u32 mask,
struct inode *inode, struct inode *dir,
const struct qstr *name)
{
struct dnotify_mark *dn_mark;
struct dnotify_struct *dn;
struct dnotify_struct **prev;
struct fown_struct *fown;
__u32 test_mask = mask & ~FS_EVENT_ON_CHILD;
/* not a dir, dnotify doesn't care */
if (!dir && !(mask & FS_ISDIR))
return 0;
dn_mark = container_of(inode_mark, struct dnotify_mark, fsn_mark);
spin_lock(&inode_mark->lock);
prev = &dn_mark->dn;
while ((dn = *prev) != NULL) {
if ((dn->dn_mask & test_mask) == 0) {
prev = &dn->dn_next;
continue;
}
fown = &dn->dn_filp->f_owner;
send_sigio(fown, dn->dn_fd, POLL_MSG);
if (dn->dn_mask & FS_DN_MULTISHOT)
prev = &dn->dn_next;
else {
*prev = dn->dn_next;
kmem_cache_free(dnotify_struct_cache, dn);
dnotify_recalc_inode_mask(inode_mark);
}
}
spin_unlock(&inode_mark->lock);
return 0;
}
static void dnotify_free_mark(struct fsnotify_mark *fsn_mark)
{
struct dnotify_mark *dn_mark = container_of(fsn_mark,
struct dnotify_mark,
fsn_mark);
BUG_ON(dn_mark->dn);
kmem_cache_free(dnotify_mark_cache, dn_mark);
}
static const struct fsnotify_ops dnotify_fsnotify_ops = {
.handle_inode_event = dnotify_handle_event,
.free_mark = dnotify_free_mark,
};
/*
* Called every time a file is closed. Looks first for a dnotify mark on the
* inode. If one is found run all of the ->dn structures attached to that
* mark for one relevant to this process closing the file and remove that
* dnotify_struct. If that was the last dnotify_struct also remove the
* fsnotify_mark.
*/
void dnotify_flush(struct file *filp, fl_owner_t id)
{
struct fsnotify_mark *fsn_mark;
struct dnotify_mark *dn_mark;
struct dnotify_struct *dn;
struct dnotify_struct **prev;
struct inode *inode;
bool free = false;
inode = file_inode(filp);
if (!S_ISDIR(inode->i_mode))
return;
fsn_mark = fsnotify_find_mark(&inode->i_fsnotify_marks, dnotify_group);
if (!fsn_mark)
return;
dn_mark = container_of(fsn_mark, struct dnotify_mark, fsn_mark);
mutex_lock(&dnotify_group->mark_mutex);
spin_lock(&fsn_mark->lock);
prev = &dn_mark->dn;
while ((dn = *prev) != NULL) {
if ((dn->dn_owner == id) && (dn->dn_filp == filp)) {
*prev = dn->dn_next;
kmem_cache_free(dnotify_struct_cache, dn);
dnotify_recalc_inode_mask(fsn_mark);
break;
}
prev = &dn->dn_next;
}
spin_unlock(&fsn_mark->lock);
/* nothing else could have found us thanks to the dnotify_groups
mark_mutex */
if (dn_mark->dn == NULL) {
fsnotify_detach_mark(fsn_mark);
free = true;
}
mutex_unlock(&dnotify_group->mark_mutex);
if (free)
fsnotify_free_mark(fsn_mark);
fsnotify_put_mark(fsn_mark);
}
/* this conversion is done only at watch creation */
static __u32 convert_arg(unsigned long arg)
{
__u32 new_mask = FS_EVENT_ON_CHILD;
if (arg & DN_MULTISHOT)
new_mask |= FS_DN_MULTISHOT;
if (arg & DN_DELETE)
new_mask |= (FS_DELETE | FS_MOVED_FROM);
if (arg & DN_MODIFY)
new_mask |= FS_MODIFY;
if (arg & DN_ACCESS)
new_mask |= FS_ACCESS;
if (arg & DN_ATTRIB)
new_mask |= FS_ATTRIB;
if (arg & DN_RENAME)
new_mask |= FS_DN_RENAME;
if (arg & DN_CREATE)
new_mask |= (FS_CREATE | FS_MOVED_TO);
return new_mask;
}
/*
* If multiple processes watch the same inode with dnotify there is only one
* dnotify mark in inode->i_fsnotify_marks but we chain a dnotify_struct
* onto that mark. This function either attaches the new dnotify_struct onto
* that list, or it |= the mask onto an existing dnofiy_struct.
*/
static int attach_dn(struct dnotify_struct *dn, struct dnotify_mark *dn_mark,
fl_owner_t id, int fd, struct file *filp, __u32 mask)
{
struct dnotify_struct *odn;
odn = dn_mark->dn;
while (odn != NULL) {
/* adding more events to existing dnofiy_struct? */
if ((odn->dn_owner == id) && (odn->dn_filp == filp)) {
odn->dn_fd = fd;
odn->dn_mask |= mask;
return -EEXIST;
}
odn = odn->dn_next;
}
dn->dn_mask = mask;
dn->dn_fd = fd;
dn->dn_filp = filp;
dn->dn_owner = id;
dn->dn_next = dn_mark->dn;
dn_mark->dn = dn;
return 0;
}
/*
* When a process calls fcntl to attach a dnotify watch to a directory it ends
* up here. Allocate both a mark for fsnotify to add and a dnotify_struct to be
* attached to the fsnotify_mark.
*/
int fcntl_dirnotify(int fd, struct file *filp, unsigned long arg)
{
struct dnotify_mark *new_dn_mark, *dn_mark;
struct fsnotify_mark *new_fsn_mark, *fsn_mark;
struct dnotify_struct *dn;
struct inode *inode;
fl_owner_t id = current->files;
struct file *f;
int destroy = 0, error = 0;
__u32 mask;
/* we use these to tell if we need to kfree */
new_fsn_mark = NULL;
dn = NULL;
if (!dir_notify_enable) {
error = -EINVAL;
goto out_err;
}
/* a 0 mask means we are explicitly removing the watch */
if ((arg & ~DN_MULTISHOT) == 0) {
dnotify_flush(filp, id);
error = 0;
goto out_err;
}
/* dnotify only works on directories */
inode = file_inode(filp);
if (!S_ISDIR(inode->i_mode)) {
error = -ENOTDIR;
goto out_err;
}
/*
* convert the userspace DN_* "arg" to the internal FS_*
* defined in fsnotify
*/
mask = convert_arg(arg);
error = security_path_notify(&filp->f_path, mask,
FSNOTIFY_OBJ_TYPE_INODE);
if (error)
goto out_err;
/* expect most fcntl to add new rather than augment old */
dn = kmem_cache_alloc(dnotify_struct_cache, GFP_KERNEL);
if (!dn) {
error = -ENOMEM;
goto out_err;
}
/* new fsnotify mark, we expect most fcntl calls to add a new mark */
new_dn_mark = kmem_cache_alloc(dnotify_mark_cache, GFP_KERNEL);
if (!new_dn_mark) {
error = -ENOMEM;
goto out_err;
}
/* set up the new_fsn_mark and new_dn_mark */
new_fsn_mark = &new_dn_mark->fsn_mark;
fsnotify_init_mark(new_fsn_mark, dnotify_group);
new_fsn_mark->mask = mask;
new_dn_mark->dn = NULL;
/* this is needed to prevent the fcntl/close race described below */
mutex_lock(&dnotify_group->mark_mutex);
/* add the new_fsn_mark or find an old one. */
fsn_mark = fsnotify_find_mark(&inode->i_fsnotify_marks, dnotify_group);
if (fsn_mark) {
dn_mark = container_of(fsn_mark, struct dnotify_mark, fsn_mark);
spin_lock(&fsn_mark->lock);
} else {
error = fsnotify_add_inode_mark_locked(new_fsn_mark, inode, 0);
if (error) {
mutex_unlock(&dnotify_group->mark_mutex);
goto out_err;
}
spin_lock(&new_fsn_mark->lock);
fsn_mark = new_fsn_mark;
dn_mark = new_dn_mark;
/* we used new_fsn_mark, so don't free it */
new_fsn_mark = NULL;
}
rcu_read_lock();
f = fcheck(fd);
rcu_read_unlock();
/* if (f != filp) means that we lost a race and another task/thread
* actually closed the fd we are still playing with before we grabbed
* the dnotify_groups mark_mutex and fsn_mark->lock. Since closing the
* fd is the only time we clean up the marks we need to get our mark
* off the list. */
if (f != filp) {
/* if we added ourselves, shoot ourselves, it's possible that
* the flush actually did shoot this fsn_mark. That's fine too
* since multiple calls to destroy_mark is perfectly safe, if
* we found a dn_mark already attached to the inode, just sod
* off silently as the flush at close time dealt with it.
*/
if (dn_mark == new_dn_mark)
destroy = 1;
error = 0;
goto out;
}
__f_setown(filp, task_pid(current), PIDTYPE_TGID, 0);
error = attach_dn(dn, dn_mark, id, fd, filp, mask);
/* !error means that we attached the dn to the dn_mark, so don't free it */
if (!error)
dn = NULL;
/* -EEXIST means that we didn't add this new dn and used an old one.
* that isn't an error (and the unused dn should be freed) */
else if (error == -EEXIST)
error = 0;
dnotify_recalc_inode_mask(fsn_mark);
out:
spin_unlock(&fsn_mark->lock);
if (destroy)
fsnotify_detach_mark(fsn_mark);
mutex_unlock(&dnotify_group->mark_mutex);
if (destroy)
fsnotify_free_mark(fsn_mark);
fsnotify_put_mark(fsn_mark);
out_err:
if (new_fsn_mark)
fsnotify_put_mark(new_fsn_mark);
if (dn)
kmem_cache_free(dnotify_struct_cache, dn);
return error;
}
static int __init dnotify_init(void)
{
dnotify_struct_cache = KMEM_CACHE(dnotify_struct,
SLAB_PANIC|SLAB_ACCOUNT);
dnotify_mark_cache = KMEM_CACHE(dnotify_mark, SLAB_PANIC|SLAB_ACCOUNT);
dnotify_group = fsnotify_alloc_group(&dnotify_fsnotify_ops);
if (IS_ERR(dnotify_group))
panic("unable to allocate fsnotify group for dnotify\n");
return 0;
}
module_init(dnotify_init)