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>

12 files changed, 15 insertions, 3 deletions

diff --git a/arch/cris/arch-v10/drivers/ds1302.c b/arch/cris/arch-v10/drivers/ds1302.c
index 884275629ef7..95aadb4a8cf1 100644
--- a/arch/cris/arch-v10/drivers/ds1302.c
+++ b/arch/cris/arch-v10/drivers/ds1302.c
@@ -387,6 +387,7 @@ print_rtc_status(void)
 static const struct file_operations rtc_fops = {
 	.owner		= THIS_MODULE,
 	.unlocked_ioctl = rtc_unlocked_ioctl,
+	.llseek		= noop_llseek,
 }; 
 
 /* Probe for the chip by writing something to its RAM and try reading it back. */
diff --git a/arch/cris/arch-v10/drivers/gpio.c b/arch/cris/arch-v10/drivers/gpio.c
index a07b6d25b0c7..a276f0811731 100644
--- a/arch/cris/arch-v10/drivers/gpio.c
+++ b/arch/cris/arch-v10/drivers/gpio.c
@@ -745,6 +745,7 @@ static const struct file_operations gpio_fops = {
 	.write          = gpio_write,
 	.open           = gpio_open,
 	.release        = gpio_release,
+	.llseek		= noop_llseek,
 };
 
 static void ioif_watcher(const unsigned int gpio_in_available,
diff --git a/arch/cris/arch-v10/drivers/i2c.c b/arch/cris/arch-v10/drivers/i2c.c
index 77a941813819..c413539d4205 100644
--- a/arch/cris/arch-v10/drivers/i2c.c
+++ b/arch/cris/arch-v10/drivers/i2c.c
@@ -617,6 +617,7 @@ static const struct file_operations i2c_fops = {
 	.unlocked_ioctl	= i2c_ioctl,
 	.open		= i2c_open,
 	.release	= i2c_release,
+	.llseek		= noop_llseek,
 };
 
 int __init
diff --git a/arch/cris/arch-v10/drivers/pcf8563.c b/arch/cris/arch-v10/drivers/pcf8563.c
index 7dcb1f85f42b..7aa6ff00a117 100644
--- a/arch/cris/arch-v10/drivers/pcf8563.c
+++ b/arch/cris/arch-v10/drivers/pcf8563.c
@@ -64,6 +64,7 @@ static int voltage_low;
 static const struct file_operations pcf8563_fops = {
 	.owner = THIS_MODULE,
 	.unlocked_ioctl = pcf8563_unlocked_ioctl,
+	.llseek		= noop_llseek,
 };
 
 unsigned char
diff --git a/arch/cris/arch-v10/drivers/sync_serial.c b/arch/cris/arch-v10/drivers/sync_serial.c
index ee2dd4323daf..e501632fa8c2 100644
--- a/arch/cris/arch-v10/drivers/sync_serial.c
+++ b/arch/cris/arch-v10/drivers/sync_serial.c
@@ -250,7 +250,8 @@ static const struct file_operations sync_serial_fops = {
 	.poll		= sync_serial_poll,
 	.unlocked_ioctl	= sync_serial_ioctl,
 	.open		= sync_serial_open,
-	.release	= sync_serial_release
+	.release	= sync_serial_release,
+	.llseek		= noop_llseek,
 };
 
 static int __init etrax_sync_serial_init(void)
diff --git a/arch/cris/arch-v32/drivers/cryptocop.c b/arch/cris/arch-v32/drivers/cryptocop.c
index b07646a30509..dcb43fddfb99 100644
--- a/arch/cris/arch-v32/drivers/cryptocop.c
+++ b/arch/cris/arch-v32/drivers/cryptocop.c
@@ -281,7 +281,8 @@ const struct file_operations cryptocop_fops = {
 	.owner		= THIS_MODULE,
 	.open		= cryptocop_open,
 	.release	= cryptocop_release,
-	.unlocked_ioctl = cryptocop_ioctl
+	.unlocked_ioctl = cryptocop_ioctl,
+	.llseek		= noop_llseek,
 };
 
 
diff --git a/arch/cris/arch-v32/drivers/i2c.c b/arch/cris/arch-v32/drivers/i2c.c
index 5a3e900c9a78..ddb23996f11a 100644
--- a/arch/cris/arch-v32/drivers/i2c.c
+++ b/arch/cris/arch-v32/drivers/i2c.c
@@ -698,6 +698,7 @@ static const struct file_operations i2c_fops = {
 	.unlocked_ioctl = i2c_ioctl,
 	.open		= i2c_open,
 	.release	= i2c_release,
+	.llseek		= noop_llseek,
 };
 
 static int __init i2c_init(void)
diff --git a/arch/cris/arch-v32/drivers/mach-a3/gpio.c b/arch/cris/arch-v32/drivers/mach-a3/gpio.c
index 2dcd27adbad4..06b24ebda410 100644
--- a/arch/cris/arch-v32/drivers/mach-a3/gpio.c
+++ b/arch/cris/arch-v32/drivers/mach-a3/gpio.c
@@ -893,6 +893,7 @@ static const struct file_operations gpio_fops = {
 	.write		= gpio_write,
 	.open		= gpio_open,
 	.release	= gpio_release,
+	.llseek		= noop_llseek,
 };
 
 #ifdef CONFIG_ETRAX_VIRTUAL_GPIO
diff --git a/arch/cris/arch-v32/drivers/mach-fs/gpio.c b/arch/cris/arch-v32/drivers/mach-fs/gpio.c
index 5ec8a7d4e7d7..0649c8bea676 100644
--- a/arch/cris/arch-v32/drivers/mach-fs/gpio.c
+++ b/arch/cris/arch-v32/drivers/mach-fs/gpio.c
@@ -870,6 +870,7 @@ static const struct file_operations gpio_fops = {
 	.write		= gpio_write,
 	.open		= gpio_open,
 	.release	= gpio_release,
+	.llseek		= noop_llseek,
 };
 
 #ifdef CONFIG_ETRAX_VIRTUAL_GPIO
diff --git a/arch/cris/arch-v32/drivers/pcf8563.c b/arch/cris/arch-v32/drivers/pcf8563.c
index bef6eb53b153..0f7b101ee5ee 100644
--- a/arch/cris/arch-v32/drivers/pcf8563.c
+++ b/arch/cris/arch-v32/drivers/pcf8563.c
@@ -60,6 +60,7 @@ static int voltage_low;
 static const struct file_operations pcf8563_fops = {
 	.owner		= THIS_MODULE,
 	.unlocked_ioctl = pcf8563_unlocked_ioctl,
+	.llseek		= noop_llseek,
 };
 
 unsigned char
diff --git a/arch/cris/arch-v32/drivers/sync_serial.c b/arch/cris/arch-v32/drivers/sync_serial.c
index ca248f3adb80..a2e8a8c39856 100644
--- a/arch/cris/arch-v32/drivers/sync_serial.c
+++ b/arch/cris/arch-v32/drivers/sync_serial.c
@@ -247,7 +247,8 @@ static const struct file_operations sync_serial_fops = {
 	.poll		= sync_serial_poll,
 	.unlocked_ioctl	= sync_serial_ioctl,
 	.open		= sync_serial_open,
-	.release	= sync_serial_release
+	.release	= sync_serial_release,
+	.llseek		= noop_llseek,
 };
 
 static int __init etrax_sync_serial_init(void)
diff --git a/arch/cris/kernel/profile.c b/arch/cris/kernel/profile.c
index 195ec5fa0dd2..b82e08615d1b 100644
--- a/arch/cris/kernel/profile.c
+++ b/arch/cris/kernel/profile.c
@@ -59,6 +59,7 @@ write_cris_profile(struct file *file, const char __user *buf,
 static const struct file_operations cris_proc_profile_operations = {
 	.read		= read_cris_profile,
 	.write		= write_cris_profile,
+	.llseek		= default_llseek,
 };
 
 static int __init init_cris_profile(void)