linux/fs/kernfs/file.c

880 lines
22 KiB
C

/*
* fs/kernfs/file.c - kernfs file 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/seq_file.h>
#include <linux/slab.h>
#include <linux/poll.h>
#include <linux/pagemap.h>
#include <linux/sched.h>
#include "kernfs-internal.h"
/*
* There's one kernfs_open_file for each open file and one kernfs_open_node
* for each kernfs_node with one or more open files.
*
* kernfs_node->attr.open points to kernfs_open_node. attr.open is
* protected by kernfs_open_node_lock.
*
* filp->private_data points to seq_file whose ->private points to
* kernfs_open_file. kernfs_open_files are chained at
* kernfs_open_node->files, which is protected by kernfs_open_file_mutex.
*/
static DEFINE_SPINLOCK(kernfs_open_node_lock);
static DEFINE_MUTEX(kernfs_open_file_mutex);
struct kernfs_open_node {
atomic_t refcnt;
atomic_t event;
wait_queue_head_t poll;
struct list_head files; /* goes through kernfs_open_file.list */
};
static struct kernfs_open_file *kernfs_of(struct file *file)
{
return ((struct seq_file *)file->private_data)->private;
}
/*
* Determine the kernfs_ops for the given kernfs_node. This function must
* be called while holding an active reference.
*/
static const struct kernfs_ops *kernfs_ops(struct kernfs_node *kn)
{
if (kn->flags & KERNFS_LOCKDEP)
lockdep_assert_held(kn);
return kn->attr.ops;
}
/*
* As kernfs_seq_stop() is also called after kernfs_seq_start() or
* kernfs_seq_next() failure, it needs to distinguish whether it's stopping
* a seq_file iteration which is fully initialized with an active reference
* or an aborted kernfs_seq_start() due to get_active failure. The
* position pointer is the only context for each seq_file iteration and
* thus the stop condition should be encoded in it. As the return value is
* directly visible to userland, ERR_PTR(-ENODEV) is the only acceptable
* choice to indicate get_active failure.
*
* Unfortunately, this is complicated due to the optional custom seq_file
* operations which may return ERR_PTR(-ENODEV) too. kernfs_seq_stop()
* can't distinguish whether ERR_PTR(-ENODEV) is from get_active failure or
* custom seq_file operations and thus can't decide whether put_active
* should be performed or not only on ERR_PTR(-ENODEV).
*
* This is worked around by factoring out the custom seq_stop() and
* put_active part into kernfs_seq_stop_active(), skipping it from
* kernfs_seq_stop() if ERR_PTR(-ENODEV) while invoking it directly after
* custom seq_file operations fail with ERR_PTR(-ENODEV) - this ensures
* that kernfs_seq_stop_active() is skipped only after get_active failure.
*/
static void kernfs_seq_stop_active(struct seq_file *sf, void *v)
{
struct kernfs_open_file *of = sf->private;
const struct kernfs_ops *ops = kernfs_ops(of->kn);
if (ops->seq_stop)
ops->seq_stop(sf, v);
kernfs_put_active(of->kn);
}
static void *kernfs_seq_start(struct seq_file *sf, loff_t *ppos)
{
struct kernfs_open_file *of = sf->private;
const struct kernfs_ops *ops;
/*
* @of->mutex nests outside active ref and is just to ensure that
* the ops aren't called concurrently for the same open file.
*/
mutex_lock(&of->mutex);
if (!kernfs_get_active(of->kn))
return ERR_PTR(-ENODEV);
ops = kernfs_ops(of->kn);
if (ops->seq_start) {
void *next = ops->seq_start(sf, ppos);
/* see the comment above kernfs_seq_stop_active() */
if (next == ERR_PTR(-ENODEV))
kernfs_seq_stop_active(sf, next);
return next;
} else {
/*
* The same behavior and code as single_open(). Returns
* !NULL if pos is at the beginning; otherwise, NULL.
*/
return NULL + !*ppos;
}
}
static void *kernfs_seq_next(struct seq_file *sf, void *v, loff_t *ppos)
{
struct kernfs_open_file *of = sf->private;
const struct kernfs_ops *ops = kernfs_ops(of->kn);
if (ops->seq_next) {
void *next = ops->seq_next(sf, v, ppos);
/* see the comment above kernfs_seq_stop_active() */
if (next == ERR_PTR(-ENODEV))
kernfs_seq_stop_active(sf, next);
return next;
} else {
/*
* The same behavior and code as single_open(), always
* terminate after the initial read.
*/
++*ppos;
return NULL;
}
}
static void kernfs_seq_stop(struct seq_file *sf, void *v)
{
struct kernfs_open_file *of = sf->private;
if (v != ERR_PTR(-ENODEV))
kernfs_seq_stop_active(sf, v);
mutex_unlock(&of->mutex);
}
static int kernfs_seq_show(struct seq_file *sf, void *v)
{
struct kernfs_open_file *of = sf->private;
of->event = atomic_read(&of->kn->attr.open->event);
return of->kn->attr.ops->seq_show(sf, v);
}
static const struct seq_operations kernfs_seq_ops = {
.start = kernfs_seq_start,
.next = kernfs_seq_next,
.stop = kernfs_seq_stop,
.show = kernfs_seq_show,
};
/*
* As reading a bin file can have side-effects, the exact offset and bytes
* specified in read(2) call should be passed to the read callback making
* it difficult to use seq_file. Implement simplistic custom buffering for
* bin files.
*/
static ssize_t kernfs_file_direct_read(struct kernfs_open_file *of,
char __user *user_buf, size_t count,
loff_t *ppos)
{
ssize_t len = min_t(size_t, count, PAGE_SIZE);
const struct kernfs_ops *ops;
char *buf;
buf = kmalloc(len, GFP_KERNEL);
if (!buf)
return -ENOMEM;
/*
* @of->mutex nests outside active ref and is just to ensure that
* the ops aren't called concurrently for the same open file.
*/
mutex_lock(&of->mutex);
if (!kernfs_get_active(of->kn)) {
len = -ENODEV;
mutex_unlock(&of->mutex);
goto out_free;
}
ops = kernfs_ops(of->kn);
if (ops->read)
len = ops->read(of, buf, len, *ppos);
else
len = -EINVAL;
kernfs_put_active(of->kn);
mutex_unlock(&of->mutex);
if (len < 0)
goto out_free;
if (copy_to_user(user_buf, buf, len)) {
len = -EFAULT;
goto out_free;
}
*ppos += len;
out_free:
kfree(buf);
return len;
}
/**
* kernfs_fop_read - kernfs vfs read callback
* @file: file pointer
* @user_buf: data to write
* @count: number of bytes
* @ppos: starting offset
*/
static ssize_t kernfs_fop_read(struct file *file, char __user *user_buf,
size_t count, loff_t *ppos)
{
struct kernfs_open_file *of = kernfs_of(file);
if (of->kn->flags & KERNFS_HAS_SEQ_SHOW)
return seq_read(file, user_buf, count, ppos);
else
return kernfs_file_direct_read(of, user_buf, count, ppos);
}
/**
* kernfs_fop_write - kernfs vfs write callback
* @file: file pointer
* @user_buf: data to write
* @count: number of bytes
* @ppos: starting offset
*
* Copy data in from userland and pass it to the matching kernfs write
* operation.
*
* There is no easy way for us to know if userspace is only doing a partial
* write, so we don't support them. We expect the entire buffer to come on
* the first write. Hint: if you're writing a value, first read the file,
* modify only the the value you're changing, then write entire buffer
* back.
*/
static ssize_t kernfs_fop_write(struct file *file, const char __user *user_buf,
size_t count, loff_t *ppos)
{
struct kernfs_open_file *of = kernfs_of(file);
const struct kernfs_ops *ops;
size_t len;
char *buf;
if (of->atomic_write_len) {
len = count;
if (len > of->atomic_write_len)
return -E2BIG;
} else {
len = min_t(size_t, count, PAGE_SIZE);
}
buf = kmalloc(len + 1, GFP_KERNEL);
if (!buf)
return -ENOMEM;
if (copy_from_user(buf, user_buf, len)) {
len = -EFAULT;
goto out_free;
}
buf[len] = '\0'; /* guarantee string termination */
/*
* @of->mutex nests outside active ref and is just to ensure that
* the ops aren't called concurrently for the same open file.
*/
mutex_lock(&of->mutex);
if (!kernfs_get_active(of->kn)) {
mutex_unlock(&of->mutex);
len = -ENODEV;
goto out_free;
}
ops = kernfs_ops(of->kn);
if (ops->write)
len = ops->write(of, buf, len, *ppos);
else
len = -EINVAL;
kernfs_put_active(of->kn);
mutex_unlock(&of->mutex);
if (len > 0)
*ppos += len;
out_free:
kfree(buf);
return len;
}
static void kernfs_vma_open(struct vm_area_struct *vma)
{
struct file *file = vma->vm_file;
struct kernfs_open_file *of = kernfs_of(file);
if (!of->vm_ops)
return;
if (!kernfs_get_active(of->kn))
return;
if (of->vm_ops->open)
of->vm_ops->open(vma);
kernfs_put_active(of->kn);
}
static int kernfs_vma_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
{
struct file *file = vma->vm_file;
struct kernfs_open_file *of = kernfs_of(file);
int ret;
if (!of->vm_ops)
return VM_FAULT_SIGBUS;
if (!kernfs_get_active(of->kn))
return VM_FAULT_SIGBUS;
ret = VM_FAULT_SIGBUS;
if (of->vm_ops->fault)
ret = of->vm_ops->fault(vma, vmf);
kernfs_put_active(of->kn);
return ret;
}
static int kernfs_vma_page_mkwrite(struct vm_area_struct *vma,
struct vm_fault *vmf)
{
struct file *file = vma->vm_file;
struct kernfs_open_file *of = kernfs_of(file);
int ret;
if (!of->vm_ops)
return VM_FAULT_SIGBUS;
if (!kernfs_get_active(of->kn))
return VM_FAULT_SIGBUS;
ret = 0;
if (of->vm_ops->page_mkwrite)
ret = of->vm_ops->page_mkwrite(vma, vmf);
else
file_update_time(file);
kernfs_put_active(of->kn);
return ret;
}
static int kernfs_vma_access(struct vm_area_struct *vma, unsigned long addr,
void *buf, int len, int write)
{
struct file *file = vma->vm_file;
struct kernfs_open_file *of = kernfs_of(file);
int ret;
if (!of->vm_ops)
return -EINVAL;
if (!kernfs_get_active(of->kn))
return -EINVAL;
ret = -EINVAL;
if (of->vm_ops->access)
ret = of->vm_ops->access(vma, addr, buf, len, write);
kernfs_put_active(of->kn);
return ret;
}
#ifdef CONFIG_NUMA
static int kernfs_vma_set_policy(struct vm_area_struct *vma,
struct mempolicy *new)
{
struct file *file = vma->vm_file;
struct kernfs_open_file *of = kernfs_of(file);
int ret;
if (!of->vm_ops)
return 0;
if (!kernfs_get_active(of->kn))
return -EINVAL;
ret = 0;
if (of->vm_ops->set_policy)
ret = of->vm_ops->set_policy(vma, new);
kernfs_put_active(of->kn);
return ret;
}
static struct mempolicy *kernfs_vma_get_policy(struct vm_area_struct *vma,
unsigned long addr)
{
struct file *file = vma->vm_file;
struct kernfs_open_file *of = kernfs_of(file);
struct mempolicy *pol;
if (!of->vm_ops)
return vma->vm_policy;
if (!kernfs_get_active(of->kn))
return vma->vm_policy;
pol = vma->vm_policy;
if (of->vm_ops->get_policy)
pol = of->vm_ops->get_policy(vma, addr);
kernfs_put_active(of->kn);
return pol;
}
static int kernfs_vma_migrate(struct vm_area_struct *vma,
const nodemask_t *from, const nodemask_t *to,
unsigned long flags)
{
struct file *file = vma->vm_file;
struct kernfs_open_file *of = kernfs_of(file);
int ret;
if (!of->vm_ops)
return 0;
if (!kernfs_get_active(of->kn))
return 0;
ret = 0;
if (of->vm_ops->migrate)
ret = of->vm_ops->migrate(vma, from, to, flags);
kernfs_put_active(of->kn);
return ret;
}
#endif
static const struct vm_operations_struct kernfs_vm_ops = {
.open = kernfs_vma_open,
.fault = kernfs_vma_fault,
.page_mkwrite = kernfs_vma_page_mkwrite,
.access = kernfs_vma_access,
#ifdef CONFIG_NUMA
.set_policy = kernfs_vma_set_policy,
.get_policy = kernfs_vma_get_policy,
.migrate = kernfs_vma_migrate,
#endif
};
static int kernfs_fop_mmap(struct file *file, struct vm_area_struct *vma)
{
struct kernfs_open_file *of = kernfs_of(file);
const struct kernfs_ops *ops;
int rc;
/*
* mmap path and of->mutex are prone to triggering spurious lockdep
* warnings and we don't want to add spurious locking dependency
* between the two. Check whether mmap is actually implemented
* without grabbing @of->mutex by testing HAS_MMAP flag. See the
* comment in kernfs_file_open() for more details.
*/
if (!(of->kn->flags & KERNFS_HAS_MMAP))
return -ENODEV;
mutex_lock(&of->mutex);
rc = -ENODEV;
if (!kernfs_get_active(of->kn))
goto out_unlock;
ops = kernfs_ops(of->kn);
rc = ops->mmap(of, vma);
if (rc)
goto out_put;
/*
* PowerPC's pci_mmap of legacy_mem uses shmem_zero_setup()
* to satisfy versions of X which crash if the mmap fails: that
* substitutes a new vm_file, and we don't then want bin_vm_ops.
*/
if (vma->vm_file != file)
goto out_put;
rc = -EINVAL;
if (of->mmapped && of->vm_ops != vma->vm_ops)
goto out_put;
/*
* It is not possible to successfully wrap close.
* So error if someone is trying to use close.
*/
rc = -EINVAL;
if (vma->vm_ops && vma->vm_ops->close)
goto out_put;
rc = 0;
of->mmapped = 1;
of->vm_ops = vma->vm_ops;
vma->vm_ops = &kernfs_vm_ops;
out_put:
kernfs_put_active(of->kn);
out_unlock:
mutex_unlock(&of->mutex);
return rc;
}
/**
* kernfs_get_open_node - get or create kernfs_open_node
* @kn: target kernfs_node
* @of: kernfs_open_file for this instance of open
*
* If @kn->attr.open exists, increment its reference count; otherwise,
* create one. @of is chained to the files list.
*
* LOCKING:
* Kernel thread context (may sleep).
*
* RETURNS:
* 0 on success, -errno on failure.
*/
static int kernfs_get_open_node(struct kernfs_node *kn,
struct kernfs_open_file *of)
{
struct kernfs_open_node *on, *new_on = NULL;
retry:
mutex_lock(&kernfs_open_file_mutex);
spin_lock_irq(&kernfs_open_node_lock);
if (!kn->attr.open && new_on) {
kn->attr.open = new_on;
new_on = NULL;
}
on = kn->attr.open;
if (on) {
atomic_inc(&on->refcnt);
list_add_tail(&of->list, &on->files);
}
spin_unlock_irq(&kernfs_open_node_lock);
mutex_unlock(&kernfs_open_file_mutex);
if (on) {
kfree(new_on);
return 0;
}
/* not there, initialize a new one and retry */
new_on = kmalloc(sizeof(*new_on), GFP_KERNEL);
if (!new_on)
return -ENOMEM;
atomic_set(&new_on->refcnt, 0);
atomic_set(&new_on->event, 1);
init_waitqueue_head(&new_on->poll);
INIT_LIST_HEAD(&new_on->files);
goto retry;
}
/**
* kernfs_put_open_node - put kernfs_open_node
* @kn: target kernfs_nodet
* @of: associated kernfs_open_file
*
* Put @kn->attr.open and unlink @of from the files list. If
* reference count reaches zero, disassociate and free it.
*
* LOCKING:
* None.
*/
static void kernfs_put_open_node(struct kernfs_node *kn,
struct kernfs_open_file *of)
{
struct kernfs_open_node *on = kn->attr.open;
unsigned long flags;
mutex_lock(&kernfs_open_file_mutex);
spin_lock_irqsave(&kernfs_open_node_lock, flags);
if (of)
list_del(&of->list);
if (atomic_dec_and_test(&on->refcnt))
kn->attr.open = NULL;
else
on = NULL;
spin_unlock_irqrestore(&kernfs_open_node_lock, flags);
mutex_unlock(&kernfs_open_file_mutex);
kfree(on);
}
static int kernfs_fop_open(struct inode *inode, struct file *file)
{
struct kernfs_node *kn = file->f_path.dentry->d_fsdata;
const struct kernfs_ops *ops;
struct kernfs_open_file *of;
bool has_read, has_write, has_mmap;
int error = -EACCES;
if (!kernfs_get_active(kn))
return -ENODEV;
ops = kernfs_ops(kn);
has_read = ops->seq_show || ops->read || ops->mmap;
has_write = ops->write || ops->mmap;
has_mmap = ops->mmap;
/* check perms and supported operations */
if ((file->f_mode & FMODE_WRITE) &&
(!(inode->i_mode & S_IWUGO) || !has_write))
goto err_out;
if ((file->f_mode & FMODE_READ) &&
(!(inode->i_mode & S_IRUGO) || !has_read))
goto err_out;
/* allocate a kernfs_open_file for the file */
error = -ENOMEM;
of = kzalloc(sizeof(struct kernfs_open_file), GFP_KERNEL);
if (!of)
goto err_out;
/*
* The following is done to give a different lockdep key to
* @of->mutex for files which implement mmap. This is a rather
* crude way to avoid false positive lockdep warning around
* mm->mmap_sem - mmap nests @of->mutex under mm->mmap_sem and
* reading /sys/block/sda/trace/act_mask grabs sr_mutex, under
* which mm->mmap_sem nests, while holding @of->mutex. As each
* open file has a separate mutex, it's okay as long as those don't
* happen on the same file. At this point, we can't easily give
* each file a separate locking class. Let's differentiate on
* whether the file has mmap or not for now.
*
* Both paths of the branch look the same. They're supposed to
* look that way and give @of->mutex different static lockdep keys.
*/
if (has_mmap)
mutex_init(&of->mutex);
else
mutex_init(&of->mutex);
of->kn = kn;
of->file = file;
/*
* Write path needs to atomic_write_len outside active reference.
* Cache it in open_file. See kernfs_fop_write() for details.
*/
of->atomic_write_len = ops->atomic_write_len;
/*
* Always instantiate seq_file even if read access doesn't use
* seq_file or is not requested. This unifies private data access
* and readable regular files are the vast majority anyway.
*/
if (ops->seq_show)
error = seq_open(file, &kernfs_seq_ops);
else
error = seq_open(file, NULL);
if (error)
goto err_free;
((struct seq_file *)file->private_data)->private = of;
/* seq_file clears PWRITE unconditionally, restore it if WRITE */
if (file->f_mode & FMODE_WRITE)
file->f_mode |= FMODE_PWRITE;
/* make sure we have open node struct */
error = kernfs_get_open_node(kn, of);
if (error)
goto err_close;
/* open succeeded, put active references */
kernfs_put_active(kn);
return 0;
err_close:
seq_release(inode, file);
err_free:
kfree(of);
err_out:
kernfs_put_active(kn);
return error;
}
static int kernfs_fop_release(struct inode *inode, struct file *filp)
{
struct kernfs_node *kn = filp->f_path.dentry->d_fsdata;
struct kernfs_open_file *of = kernfs_of(filp);
kernfs_put_open_node(kn, of);
seq_release(inode, filp);
kfree(of);
return 0;
}
void kernfs_unmap_bin_file(struct kernfs_node *kn)
{
struct kernfs_open_node *on;
struct kernfs_open_file *of;
if (!(kn->flags & KERNFS_HAS_MMAP))
return;
spin_lock_irq(&kernfs_open_node_lock);
on = kn->attr.open;
if (on)
atomic_inc(&on->refcnt);
spin_unlock_irq(&kernfs_open_node_lock);
if (!on)
return;
mutex_lock(&kernfs_open_file_mutex);
list_for_each_entry(of, &on->files, list) {
struct inode *inode = file_inode(of->file);
unmap_mapping_range(inode->i_mapping, 0, 0, 1);
}
mutex_unlock(&kernfs_open_file_mutex);
kernfs_put_open_node(kn, NULL);
}
/*
* Kernfs attribute files are pollable. The idea is that you read
* the content and then you use 'poll' or 'select' to wait for
* the content to change. When the content changes (assuming the
* manager for the kobject supports notification), poll will
* return POLLERR|POLLPRI, and select will return the fd whether
* it is waiting for read, write, or exceptions.
* Once poll/select indicates that the value has changed, you
* need to close and re-open the file, or seek to 0 and read again.
* Reminder: this only works for attributes which actively support
* it, and it is not possible to test an attribute from userspace
* to see if it supports poll (Neither 'poll' nor 'select' return
* an appropriate error code). When in doubt, set a suitable timeout value.
*/
static unsigned int kernfs_fop_poll(struct file *filp, poll_table *wait)
{
struct kernfs_open_file *of = kernfs_of(filp);
struct kernfs_node *kn = filp->f_path.dentry->d_fsdata;
struct kernfs_open_node *on = kn->attr.open;
/* need parent for the kobj, grab both */
if (!kernfs_get_active(kn))
goto trigger;
poll_wait(filp, &on->poll, wait);
kernfs_put_active(kn);
if (of->event != atomic_read(&on->event))
goto trigger;
return DEFAULT_POLLMASK;
trigger:
return DEFAULT_POLLMASK|POLLERR|POLLPRI;
}
/**
* kernfs_notify - notify a kernfs file
* @kn: file to notify
*
* Notify @kn such that poll(2) on @kn wakes up.
*/
void kernfs_notify(struct kernfs_node *kn)
{
struct kernfs_open_node *on;
unsigned long flags;
spin_lock_irqsave(&kernfs_open_node_lock, flags);
if (!WARN_ON(kernfs_type(kn) != KERNFS_FILE)) {
on = kn->attr.open;
if (on) {
atomic_inc(&on->event);
wake_up_interruptible(&on->poll);
}
}
spin_unlock_irqrestore(&kernfs_open_node_lock, flags);
}
EXPORT_SYMBOL_GPL(kernfs_notify);
const struct file_operations kernfs_file_fops = {
.read = kernfs_fop_read,
.write = kernfs_fop_write,
.llseek = generic_file_llseek,
.mmap = kernfs_fop_mmap,
.open = kernfs_fop_open,
.release = kernfs_fop_release,
.poll = kernfs_fop_poll,
};
/**
* __kernfs_create_file - kernfs internal function to create a file
* @parent: directory to create the file in
* @name: name of the file
* @mode: mode of the file
* @size: size of the file
* @ops: kernfs operations for the file
* @priv: private data for the file
* @ns: optional namespace tag of the file
* @static_name: don't copy file name
* @key: lockdep key for the file's active_ref, %NULL to disable lockdep
*
* Returns the created node on success, ERR_PTR() value on error.
*/
struct kernfs_node *__kernfs_create_file(struct kernfs_node *parent,
const char *name,
umode_t mode, loff_t size,
const struct kernfs_ops *ops,
void *priv, const void *ns,
bool name_is_static,
struct lock_class_key *key)
{
struct kernfs_node *kn;
unsigned flags;
int rc;
flags = KERNFS_FILE;
if (name_is_static)
flags |= KERNFS_STATIC_NAME;
kn = kernfs_new_node(parent, name, (mode & S_IALLUGO) | S_IFREG, flags);
if (!kn)
return ERR_PTR(-ENOMEM);
kn->attr.ops = ops;
kn->attr.size = size;
kn->ns = ns;
kn->priv = priv;
#ifdef CONFIG_DEBUG_LOCK_ALLOC
if (key) {
lockdep_init_map(&kn->dep_map, "s_active", key, 0);
kn->flags |= KERNFS_LOCKDEP;
}
#endif
/*
* kn->attr.ops is accesible only while holding active ref. We
* need to know whether some ops are implemented outside active
* ref. Cache their existence in flags.
*/
if (ops->seq_show)
kn->flags |= KERNFS_HAS_SEQ_SHOW;
if (ops->mmap)
kn->flags |= KERNFS_HAS_MMAP;
rc = kernfs_add_one(kn);
if (rc) {
kernfs_put(kn);
return ERR_PTR(rc);
}
return kn;
}