linux/fs/fuse/cuse.c
Arnd Bergmann 6038f373a3 llseek: automatically add .llseek fop
All file_operations should get a .llseek operation so we can make
nonseekable_open the default for future file operations without a
.llseek pointer.

The three cases that we can automatically detect are no_llseek, seq_lseek
and default_llseek. For cases where we can we can automatically prove that
the file offset is always ignored, we use noop_llseek, which maintains
the current behavior of not returning an error from a seek.

New drivers should normally not use noop_llseek but instead use no_llseek
and call nonseekable_open at open time.  Existing drivers can be converted
to do the same when the maintainer knows for certain that no user code
relies on calling seek on the device file.

The generated code is often incorrectly indented and right now contains
comments that clarify for each added line why a specific variant was
chosen. In the version that gets submitted upstream, the comments will
be gone and I will manually fix the indentation, because there does not
seem to be a way to do that using coccinelle.

Some amount of new code is currently sitting in linux-next that should get
the same modifications, which I will do at the end of the merge window.

Many thanks to Julia Lawall for helping me learn to write a semantic
patch that does all this.

===== begin semantic patch =====
// This adds an llseek= method to all file operations,
// as a preparation for making no_llseek the default.
//
// The rules are
// - use no_llseek explicitly if we do nonseekable_open
// - use seq_lseek for sequential files
// - use default_llseek if we know we access f_pos
// - use noop_llseek if we know we don't access f_pos,
//   but we still want to allow users to call lseek
//
@ open1 exists @
identifier nested_open;
@@
nested_open(...)
{
<+...
nonseekable_open(...)
...+>
}

@ open exists@
identifier open_f;
identifier i, f;
identifier open1.nested_open;
@@
int open_f(struct inode *i, struct file *f)
{
<+...
(
nonseekable_open(...)
|
nested_open(...)
)
...+>
}

@ read disable optional_qualifier exists @
identifier read_f;
identifier f, p, s, off;
type ssize_t, size_t, loff_t;
expression E;
identifier func;
@@
ssize_t read_f(struct file *f, char *p, size_t s, loff_t *off)
{
<+...
(
   *off = E
|
   *off += E
|
   func(..., off, ...)
|
   E = *off
)
...+>
}

@ read_no_fpos disable optional_qualifier exists @
identifier read_f;
identifier f, p, s, off;
type ssize_t, size_t, loff_t;
@@
ssize_t read_f(struct file *f, char *p, size_t s, loff_t *off)
{
... when != off
}

@ write @
identifier write_f;
identifier f, p, s, off;
type ssize_t, size_t, loff_t;
expression E;
identifier func;
@@
ssize_t write_f(struct file *f, const char *p, size_t s, loff_t *off)
{
<+...
(
  *off = E
|
  *off += E
|
  func(..., off, ...)
|
  E = *off
)
...+>
}

@ write_no_fpos @
identifier write_f;
identifier f, p, s, off;
type ssize_t, size_t, loff_t;
@@
ssize_t write_f(struct file *f, const char *p, size_t s, loff_t *off)
{
... when != off
}

@ fops0 @
identifier fops;
@@
struct file_operations fops = {
 ...
};

@ has_llseek depends on fops0 @
identifier fops0.fops;
identifier llseek_f;
@@
struct file_operations fops = {
...
 .llseek = llseek_f,
...
};

@ has_read depends on fops0 @
identifier fops0.fops;
identifier read_f;
@@
struct file_operations fops = {
...
 .read = read_f,
...
};

@ has_write depends on fops0 @
identifier fops0.fops;
identifier write_f;
@@
struct file_operations fops = {
...
 .write = write_f,
...
};

@ has_open depends on fops0 @
identifier fops0.fops;
identifier open_f;
@@
struct file_operations fops = {
...
 .open = open_f,
...
};

// use no_llseek if we call nonseekable_open
////////////////////////////////////////////
@ nonseekable1 depends on !has_llseek && has_open @
identifier fops0.fops;
identifier nso ~= "nonseekable_open";
@@
struct file_operations fops = {
...  .open = nso, ...
+.llseek = no_llseek, /* nonseekable */
};

@ nonseekable2 depends on !has_llseek @
identifier fops0.fops;
identifier open.open_f;
@@
struct file_operations fops = {
...  .open = open_f, ...
+.llseek = no_llseek, /* open uses nonseekable */
};

// use seq_lseek for sequential files
/////////////////////////////////////
@ seq depends on !has_llseek @
identifier fops0.fops;
identifier sr ~= "seq_read";
@@
struct file_operations fops = {
...  .read = sr, ...
+.llseek = seq_lseek, /* we have seq_read */
};

// use default_llseek if there is a readdir
///////////////////////////////////////////
@ fops1 depends on !has_llseek && !nonseekable1 && !nonseekable2 && !seq @
identifier fops0.fops;
identifier readdir_e;
@@
// any other fop is used that changes pos
struct file_operations fops = {
... .readdir = readdir_e, ...
+.llseek = default_llseek, /* readdir is present */
};

// use default_llseek if at least one of read/write touches f_pos
/////////////////////////////////////////////////////////////////
@ fops2 depends on !fops1 && !has_llseek && !nonseekable1 && !nonseekable2 && !seq @
identifier fops0.fops;
identifier read.read_f;
@@
// read fops use offset
struct file_operations fops = {
... .read = read_f, ...
+.llseek = default_llseek, /* read accesses f_pos */
};

@ fops3 depends on !fops1 && !fops2 && !has_llseek && !nonseekable1 && !nonseekable2 && !seq @
identifier fops0.fops;
identifier write.write_f;
@@
// write fops use offset
struct file_operations fops = {
... .write = write_f, ...
+	.llseek = default_llseek, /* write accesses f_pos */
};

// Use noop_llseek if neither read nor write accesses f_pos
///////////////////////////////////////////////////////////

@ fops4 depends on !fops1 && !fops2 && !fops3 && !has_llseek && !nonseekable1 && !nonseekable2 && !seq @
identifier fops0.fops;
identifier read_no_fpos.read_f;
identifier write_no_fpos.write_f;
@@
// write fops use offset
struct file_operations fops = {
...
 .write = write_f,
 .read = read_f,
...
+.llseek = noop_llseek, /* read and write both use no f_pos */
};

@ depends on has_write && !has_read && !fops1 && !fops2 && !has_llseek && !nonseekable1 && !nonseekable2 && !seq @
identifier fops0.fops;
identifier write_no_fpos.write_f;
@@
struct file_operations fops = {
... .write = write_f, ...
+.llseek = noop_llseek, /* write uses no f_pos */
};

@ depends on has_read && !has_write && !fops1 && !fops2 && !has_llseek && !nonseekable1 && !nonseekable2 && !seq @
identifier fops0.fops;
identifier read_no_fpos.read_f;
@@
struct file_operations fops = {
... .read = read_f, ...
+.llseek = noop_llseek, /* read uses no f_pos */
};

@ depends on !has_read && !has_write && !fops1 && !fops2 && !has_llseek && !nonseekable1 && !nonseekable2 && !seq @
identifier fops0.fops;
@@
struct file_operations fops = {
...
+.llseek = noop_llseek, /* no read or write fn */
};
===== End semantic patch =====

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Julia Lawall <julia@diku.dk>
Cc: Christoph Hellwig <hch@infradead.org>
2010-10-15 15:53:27 +02:00

613 lines
15 KiB
C

/*
* CUSE: Character device in Userspace
*
* Copyright (C) 2008-2009 SUSE Linux Products GmbH
* Copyright (C) 2008-2009 Tejun Heo <tj@kernel.org>
*
* This file is released under the GPLv2.
*
* CUSE enables character devices to be implemented from userland much
* like FUSE allows filesystems. On initialization /dev/cuse is
* created. By opening the file and replying to the CUSE_INIT request
* userland CUSE server can create a character device. After that the
* operation is very similar to FUSE.
*
* A CUSE instance involves the following objects.
*
* cuse_conn : contains fuse_conn and serves as bonding structure
* channel : file handle connected to the userland CUSE server
* cdev : the implemented character device
* dev : generic device for cdev
*
* Note that 'channel' is what 'dev' is in FUSE. As CUSE deals with
* devices, it's called 'channel' to reduce confusion.
*
* channel determines when the character device dies. When channel is
* closed, everything begins to destruct. The cuse_conn is taken off
* the lookup table preventing further access from cdev, cdev and
* generic device are removed and the base reference of cuse_conn is
* put.
*
* On each open, the matching cuse_conn is looked up and if found an
* additional reference is taken which is released when the file is
* closed.
*/
#include <linux/fuse.h>
#include <linux/cdev.h>
#include <linux/device.h>
#include <linux/file.h>
#include <linux/fs.h>
#include <linux/kdev_t.h>
#include <linux/kthread.h>
#include <linux/list.h>
#include <linux/magic.h>
#include <linux/miscdevice.h>
#include <linux/mutex.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/stat.h>
#include "fuse_i.h"
#define CUSE_CONNTBL_LEN 64
struct cuse_conn {
struct list_head list; /* linked on cuse_conntbl */
struct fuse_conn fc; /* fuse connection */
struct cdev *cdev; /* associated character device */
struct device *dev; /* device representing @cdev */
/* init parameters, set once during initialization */
bool unrestricted_ioctl;
};
static DEFINE_SPINLOCK(cuse_lock); /* protects cuse_conntbl */
static struct list_head cuse_conntbl[CUSE_CONNTBL_LEN];
static struct class *cuse_class;
static struct cuse_conn *fc_to_cc(struct fuse_conn *fc)
{
return container_of(fc, struct cuse_conn, fc);
}
static struct list_head *cuse_conntbl_head(dev_t devt)
{
return &cuse_conntbl[(MAJOR(devt) + MINOR(devt)) % CUSE_CONNTBL_LEN];
}
/**************************************************************************
* CUSE frontend operations
*
* These are file operations for the character device.
*
* On open, CUSE opens a file from the FUSE mnt and stores it to
* private_data of the open file. All other ops call FUSE ops on the
* FUSE file.
*/
static ssize_t cuse_read(struct file *file, char __user *buf, size_t count,
loff_t *ppos)
{
loff_t pos = 0;
return fuse_direct_io(file, buf, count, &pos, 0);
}
static ssize_t cuse_write(struct file *file, const char __user *buf,
size_t count, loff_t *ppos)
{
loff_t pos = 0;
/*
* No locking or generic_write_checks(), the server is
* responsible for locking and sanity checks.
*/
return fuse_direct_io(file, buf, count, &pos, 1);
}
static int cuse_open(struct inode *inode, struct file *file)
{
dev_t devt = inode->i_cdev->dev;
struct cuse_conn *cc = NULL, *pos;
int rc;
/* look up and get the connection */
spin_lock(&cuse_lock);
list_for_each_entry(pos, cuse_conntbl_head(devt), list)
if (pos->dev->devt == devt) {
fuse_conn_get(&pos->fc);
cc = pos;
break;
}
spin_unlock(&cuse_lock);
/* dead? */
if (!cc)
return -ENODEV;
/*
* Generic permission check is already done against the chrdev
* file, proceed to open.
*/
rc = fuse_do_open(&cc->fc, 0, file, 0);
if (rc)
fuse_conn_put(&cc->fc);
return rc;
}
static int cuse_release(struct inode *inode, struct file *file)
{
struct fuse_file *ff = file->private_data;
struct fuse_conn *fc = ff->fc;
fuse_sync_release(ff, file->f_flags);
fuse_conn_put(fc);
return 0;
}
static long cuse_file_ioctl(struct file *file, unsigned int cmd,
unsigned long arg)
{
struct fuse_file *ff = file->private_data;
struct cuse_conn *cc = fc_to_cc(ff->fc);
unsigned int flags = 0;
if (cc->unrestricted_ioctl)
flags |= FUSE_IOCTL_UNRESTRICTED;
return fuse_do_ioctl(file, cmd, arg, flags);
}
static long cuse_file_compat_ioctl(struct file *file, unsigned int cmd,
unsigned long arg)
{
struct fuse_file *ff = file->private_data;
struct cuse_conn *cc = fc_to_cc(ff->fc);
unsigned int flags = FUSE_IOCTL_COMPAT;
if (cc->unrestricted_ioctl)
flags |= FUSE_IOCTL_UNRESTRICTED;
return fuse_do_ioctl(file, cmd, arg, flags);
}
static const struct file_operations cuse_frontend_fops = {
.owner = THIS_MODULE,
.read = cuse_read,
.write = cuse_write,
.open = cuse_open,
.release = cuse_release,
.unlocked_ioctl = cuse_file_ioctl,
.compat_ioctl = cuse_file_compat_ioctl,
.poll = fuse_file_poll,
.llseek = noop_llseek,
};
/**************************************************************************
* CUSE channel initialization and destruction
*/
struct cuse_devinfo {
const char *name;
};
/**
* cuse_parse_one - parse one key=value pair
* @pp: i/o parameter for the current position
* @end: points to one past the end of the packed string
* @keyp: out parameter for key
* @valp: out parameter for value
*
* *@pp points to packed strings - "key0=val0\0key1=val1\0" which ends
* at @end - 1. This function parses one pair and set *@keyp to the
* start of the key and *@valp to the start of the value. Note that
* the original string is modified such that the key string is
* terminated with '\0'. *@pp is updated to point to the next string.
*
* RETURNS:
* 1 on successful parse, 0 on EOF, -errno on failure.
*/
static int cuse_parse_one(char **pp, char *end, char **keyp, char **valp)
{
char *p = *pp;
char *key, *val;
while (p < end && *p == '\0')
p++;
if (p == end)
return 0;
if (end[-1] != '\0') {
printk(KERN_ERR "CUSE: info not properly terminated\n");
return -EINVAL;
}
key = val = p;
p += strlen(p);
if (valp) {
strsep(&val, "=");
if (!val)
val = key + strlen(key);
key = strstrip(key);
val = strstrip(val);
} else
key = strstrip(key);
if (!strlen(key)) {
printk(KERN_ERR "CUSE: zero length info key specified\n");
return -EINVAL;
}
*pp = p;
*keyp = key;
if (valp)
*valp = val;
return 1;
}
/**
* cuse_parse_dev_info - parse device info
* @p: device info string
* @len: length of device info string
* @devinfo: out parameter for parsed device info
*
* Parse @p to extract device info and store it into @devinfo. String
* pointed to by @p is modified by parsing and @devinfo points into
* them, so @p shouldn't be freed while @devinfo is in use.
*
* RETURNS:
* 0 on success, -errno on failure.
*/
static int cuse_parse_devinfo(char *p, size_t len, struct cuse_devinfo *devinfo)
{
char *end = p + len;
char *key, *val;
int rc;
while (true) {
rc = cuse_parse_one(&p, end, &key, &val);
if (rc < 0)
return rc;
if (!rc)
break;
if (strcmp(key, "DEVNAME") == 0)
devinfo->name = val;
else
printk(KERN_WARNING "CUSE: unknown device info \"%s\"\n",
key);
}
if (!devinfo->name || !strlen(devinfo->name)) {
printk(KERN_ERR "CUSE: DEVNAME unspecified\n");
return -EINVAL;
}
return 0;
}
static void cuse_gendev_release(struct device *dev)
{
kfree(dev);
}
/**
* cuse_process_init_reply - finish initializing CUSE channel
*
* This function creates the character device and sets up all the
* required data structures for it. Please read the comment at the
* top of this file for high level overview.
*/
static void cuse_process_init_reply(struct fuse_conn *fc, struct fuse_req *req)
{
struct cuse_conn *cc = fc_to_cc(fc);
struct cuse_init_out *arg = &req->misc.cuse_init_out;
struct page *page = req->pages[0];
struct cuse_devinfo devinfo = { };
struct device *dev;
struct cdev *cdev;
dev_t devt;
int rc;
if (req->out.h.error ||
arg->major != FUSE_KERNEL_VERSION || arg->minor < 11) {
goto err;
}
fc->minor = arg->minor;
fc->max_read = max_t(unsigned, arg->max_read, 4096);
fc->max_write = max_t(unsigned, arg->max_write, 4096);
/* parse init reply */
cc->unrestricted_ioctl = arg->flags & CUSE_UNRESTRICTED_IOCTL;
rc = cuse_parse_devinfo(page_address(page), req->out.args[1].size,
&devinfo);
if (rc)
goto err;
/* determine and reserve devt */
devt = MKDEV(arg->dev_major, arg->dev_minor);
if (!MAJOR(devt))
rc = alloc_chrdev_region(&devt, MINOR(devt), 1, devinfo.name);
else
rc = register_chrdev_region(devt, 1, devinfo.name);
if (rc) {
printk(KERN_ERR "CUSE: failed to register chrdev region\n");
goto err;
}
/* devt determined, create device */
rc = -ENOMEM;
dev = kzalloc(sizeof(*dev), GFP_KERNEL);
if (!dev)
goto err_region;
device_initialize(dev);
dev_set_uevent_suppress(dev, 1);
dev->class = cuse_class;
dev->devt = devt;
dev->release = cuse_gendev_release;
dev_set_drvdata(dev, cc);
dev_set_name(dev, "%s", devinfo.name);
rc = device_add(dev);
if (rc)
goto err_device;
/* register cdev */
rc = -ENOMEM;
cdev = cdev_alloc();
if (!cdev)
goto err_device;
cdev->owner = THIS_MODULE;
cdev->ops = &cuse_frontend_fops;
rc = cdev_add(cdev, devt, 1);
if (rc)
goto err_cdev;
cc->dev = dev;
cc->cdev = cdev;
/* make the device available */
spin_lock(&cuse_lock);
list_add(&cc->list, cuse_conntbl_head(devt));
spin_unlock(&cuse_lock);
/* announce device availability */
dev_set_uevent_suppress(dev, 0);
kobject_uevent(&dev->kobj, KOBJ_ADD);
out:
__free_page(page);
return;
err_cdev:
cdev_del(cdev);
err_device:
put_device(dev);
err_region:
unregister_chrdev_region(devt, 1);
err:
fc->conn_error = 1;
goto out;
}
static int cuse_send_init(struct cuse_conn *cc)
{
int rc;
struct fuse_req *req;
struct page *page;
struct fuse_conn *fc = &cc->fc;
struct cuse_init_in *arg;
BUILD_BUG_ON(CUSE_INIT_INFO_MAX > PAGE_SIZE);
req = fuse_get_req(fc);
if (IS_ERR(req)) {
rc = PTR_ERR(req);
goto err;
}
rc = -ENOMEM;
page = alloc_page(GFP_KERNEL | __GFP_ZERO);
if (!page)
goto err_put_req;
arg = &req->misc.cuse_init_in;
arg->major = FUSE_KERNEL_VERSION;
arg->minor = FUSE_KERNEL_MINOR_VERSION;
arg->flags |= CUSE_UNRESTRICTED_IOCTL;
req->in.h.opcode = CUSE_INIT;
req->in.numargs = 1;
req->in.args[0].size = sizeof(struct cuse_init_in);
req->in.args[0].value = arg;
req->out.numargs = 2;
req->out.args[0].size = sizeof(struct cuse_init_out);
req->out.args[0].value = &req->misc.cuse_init_out;
req->out.args[1].size = CUSE_INIT_INFO_MAX;
req->out.argvar = 1;
req->out.argpages = 1;
req->pages[0] = page;
req->num_pages = 1;
req->end = cuse_process_init_reply;
fuse_request_send_background(fc, req);
return 0;
err_put_req:
fuse_put_request(fc, req);
err:
return rc;
}
static void cuse_fc_release(struct fuse_conn *fc)
{
struct cuse_conn *cc = fc_to_cc(fc);
kfree(cc);
}
/**
* cuse_channel_open - open method for /dev/cuse
* @inode: inode for /dev/cuse
* @file: file struct being opened
*
* Userland CUSE server can create a CUSE device by opening /dev/cuse
* and replying to the initilaization request kernel sends. This
* function is responsible for handling CUSE device initialization.
* Because the fd opened by this function is used during
* initialization, this function only creates cuse_conn and sends
* init. The rest is delegated to a kthread.
*
* RETURNS:
* 0 on success, -errno on failure.
*/
static int cuse_channel_open(struct inode *inode, struct file *file)
{
struct cuse_conn *cc;
int rc;
/* set up cuse_conn */
cc = kzalloc(sizeof(*cc), GFP_KERNEL);
if (!cc)
return -ENOMEM;
fuse_conn_init(&cc->fc);
INIT_LIST_HEAD(&cc->list);
cc->fc.release = cuse_fc_release;
cc->fc.connected = 1;
cc->fc.blocked = 0;
rc = cuse_send_init(cc);
if (rc) {
fuse_conn_put(&cc->fc);
return rc;
}
file->private_data = &cc->fc; /* channel owns base reference to cc */
return 0;
}
/**
* cuse_channel_release - release method for /dev/cuse
* @inode: inode for /dev/cuse
* @file: file struct being closed
*
* Disconnect the channel, deregister CUSE device and initiate
* destruction by putting the default reference.
*
* RETURNS:
* 0 on success, -errno on failure.
*/
static int cuse_channel_release(struct inode *inode, struct file *file)
{
struct cuse_conn *cc = fc_to_cc(file->private_data);
int rc;
/* remove from the conntbl, no more access from this point on */
spin_lock(&cuse_lock);
list_del_init(&cc->list);
spin_unlock(&cuse_lock);
/* remove device */
if (cc->dev)
device_unregister(cc->dev);
if (cc->cdev) {
unregister_chrdev_region(cc->cdev->dev, 1);
cdev_del(cc->cdev);
}
/* kill connection and shutdown channel */
fuse_conn_kill(&cc->fc);
rc = fuse_dev_release(inode, file); /* puts the base reference */
return rc;
}
static struct file_operations cuse_channel_fops; /* initialized during init */
/**************************************************************************
* Misc stuff and module initializatiion
*
* CUSE exports the same set of attributes to sysfs as fusectl.
*/
static ssize_t cuse_class_waiting_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
struct cuse_conn *cc = dev_get_drvdata(dev);
return sprintf(buf, "%d\n", atomic_read(&cc->fc.num_waiting));
}
static ssize_t cuse_class_abort_store(struct device *dev,
struct device_attribute *attr,
const char *buf, size_t count)
{
struct cuse_conn *cc = dev_get_drvdata(dev);
fuse_abort_conn(&cc->fc);
return count;
}
static struct device_attribute cuse_class_dev_attrs[] = {
__ATTR(waiting, S_IFREG | 0400, cuse_class_waiting_show, NULL),
__ATTR(abort, S_IFREG | 0200, NULL, cuse_class_abort_store),
{ }
};
static struct miscdevice cuse_miscdev = {
.minor = MISC_DYNAMIC_MINOR,
.name = "cuse",
.fops = &cuse_channel_fops,
};
static int __init cuse_init(void)
{
int i, rc;
/* init conntbl */
for (i = 0; i < CUSE_CONNTBL_LEN; i++)
INIT_LIST_HEAD(&cuse_conntbl[i]);
/* inherit and extend fuse_dev_operations */
cuse_channel_fops = fuse_dev_operations;
cuse_channel_fops.owner = THIS_MODULE;
cuse_channel_fops.open = cuse_channel_open;
cuse_channel_fops.release = cuse_channel_release;
cuse_class = class_create(THIS_MODULE, "cuse");
if (IS_ERR(cuse_class))
return PTR_ERR(cuse_class);
cuse_class->dev_attrs = cuse_class_dev_attrs;
rc = misc_register(&cuse_miscdev);
if (rc) {
class_destroy(cuse_class);
return rc;
}
return 0;
}
static void __exit cuse_exit(void)
{
misc_deregister(&cuse_miscdev);
class_destroy(cuse_class);
}
module_init(cuse_init);
module_exit(cuse_exit);
MODULE_AUTHOR("Tejun Heo <tj@kernel.org>");
MODULE_DESCRIPTION("Character device in Userspace");
MODULE_LICENSE("GPL");