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>

16 files changed, 23 insertions, 2 deletions

diff --git a/drivers/usb/class/cdc-wdm.c b/drivers/usb/class/cdc-wdm.c
index 094c76b5de17..6ee4451bfe2d 100644
--- a/drivers/usb/class/cdc-wdm.c
+++ b/drivers/usb/class/cdc-wdm.c
@@ -584,7 +584,8 @@ static const struct file_operations wdm_fops = {
 	.open =		wdm_open,
 	.flush =	wdm_flush,
 	.release =	wdm_release,
-	.poll =		wdm_poll
+	.poll =		wdm_poll,
+	.llseek =	noop_llseek,
 };
 
 static struct usb_class_driver wdm_class = {
diff --git a/drivers/usb/class/usblp.c b/drivers/usb/class/usblp.c
index e325162859b0..9eca4053312e 100644
--- a/drivers/usb/class/usblp.c
+++ b/drivers/usb/class/usblp.c
@@ -1043,6 +1043,7 @@ static const struct file_operations usblp_fops = {
 	.compat_ioctl =		usblp_ioctl,
 	.open =		usblp_open,
 	.release =	usblp_release,
+	.llseek =	noop_llseek,
 };
 
 static char *usblp_devnode(struct device *dev, mode_t *mode)
diff --git a/drivers/usb/class/usbtmc.c b/drivers/usb/class/usbtmc.c
index 3e7c1b800ebb..6a54634ab823 100644
--- a/drivers/usb/class/usbtmc.c
+++ b/drivers/usb/class/usbtmc.c
@@ -987,6 +987,7 @@ static const struct file_operations fops = {
 	.open		= usbtmc_open,
 	.release	= usbtmc_release,
 	.unlocked_ioctl	= usbtmc_ioctl,
+	.llseek		= default_llseek,
 };
 
 static struct usb_class_driver usbtmc_class = {
diff --git a/drivers/usb/core/file.c b/drivers/usb/core/file.c
index f06f5dbc8cdc..580bcd396839 100644
--- a/drivers/usb/core/file.c
+++ b/drivers/usb/core/file.c
@@ -59,6 +59,7 @@ static int usb_open(struct inode * inode, struct file * file)
 static const struct file_operations usb_fops = {
 	.owner =	THIS_MODULE,
 	.open =		usb_open,
+	.llseek =	noop_llseek,
 };
 
 static struct usb_class {
diff --git a/drivers/usb/gadget/f_hid.c b/drivers/usb/gadget/f_hid.c
index 53e120208e99..2b98bd26364b 100644
--- a/drivers/usb/gadget/f_hid.c
+++ b/drivers/usb/gadget/f_hid.c
@@ -451,6 +451,7 @@ const struct file_operations f_hidg_fops = {
 	.write		= f_hidg_write,
 	.read		= f_hidg_read,
 	.poll		= f_hidg_poll,
+	.llseek		= noop_llseek,
 };
 
 static int __init hidg_bind(struct usb_configuration *c, struct usb_function *f)
diff --git a/drivers/usb/gadget/printer.c b/drivers/usb/gadget/printer.c
index cf241c371a71..327a92a137b4 100644
--- a/drivers/usb/gadget/printer.c
+++ b/drivers/usb/gadget/printer.c
@@ -884,7 +884,8 @@ static const struct file_operations printer_io_operations = {
 	.fsync =	printer_fsync,
 	.poll =		printer_poll,
 	.unlocked_ioctl = printer_ioctl,
-	.release =	printer_close
+	.release =	printer_close,
+	.llseek =	noop_llseek,
 };
 
 /*-------------------------------------------------------------------------*/
diff --git a/drivers/usb/host/ehci-dbg.c b/drivers/usb/host/ehci-dbg.c
index 76b7fd2d838a..86afdc73322f 100644
--- a/drivers/usb/host/ehci-dbg.c
+++ b/drivers/usb/host/ehci-dbg.c
@@ -369,18 +369,21 @@ static const struct file_operations debug_async_fops = {
 	.open		= debug_async_open,
 	.read		= debug_output,
 	.release	= debug_close,
+	.llseek		= default_llseek,
 };
 static const struct file_operations debug_periodic_fops = {
 	.owner		= THIS_MODULE,
 	.open		= debug_periodic_open,
 	.read		= debug_output,
 	.release	= debug_close,
+	.llseek		= default_llseek,
 };
 static const struct file_operations debug_registers_fops = {
 	.owner		= THIS_MODULE,
 	.open		= debug_registers_open,
 	.read		= debug_output,
 	.release	= debug_close,
+	.llseek		= default_llseek,
 };
 static const struct file_operations debug_lpm_fops = {
 	.owner		= THIS_MODULE,
@@ -388,6 +391,7 @@ static const struct file_operations debug_lpm_fops = {
 	.read		= debug_lpm_read,
 	.write		= debug_lpm_write,
 	.release	= debug_lpm_close,
+	.llseek		= noop_llseek,
 };
 
 static struct dentry *ehci_debug_root;
diff --git a/drivers/usb/host/ohci-dbg.c b/drivers/usb/host/ohci-dbg.c
index 36abd2baa3ea..d7d34492934a 100644
--- a/drivers/usb/host/ohci-dbg.c
+++ b/drivers/usb/host/ohci-dbg.c
@@ -413,18 +413,21 @@ static const struct file_operations debug_async_fops = {
 	.open		= debug_async_open,
 	.read		= debug_output,
 	.release	= debug_close,
+	.llseek		= default_llseek,
 };
 static const struct file_operations debug_periodic_fops = {
 	.owner		= THIS_MODULE,
 	.open		= debug_periodic_open,
 	.read		= debug_output,
 	.release	= debug_close,
+	.llseek		= default_llseek,
 };
 static const struct file_operations debug_registers_fops = {
 	.owner		= THIS_MODULE,
 	.open		= debug_registers_open,
 	.read		= debug_output,
 	.release	= debug_close,
+	.llseek		= default_llseek,
 };
 
 static struct dentry *ohci_debug_root;
diff --git a/drivers/usb/image/mdc800.c b/drivers/usb/image/mdc800.c
index e192e8f7c560..575b56c79e97 100644
--- a/drivers/usb/image/mdc800.c
+++ b/drivers/usb/image/mdc800.c
@@ -963,6 +963,7 @@ static const struct file_operations mdc800_device_ops =
 	.write =	mdc800_device_write,
 	.open =		mdc800_device_open,
 	.release =	mdc800_device_release,
+	.llseek =	noop_llseek,
 };
 
 
diff --git a/drivers/usb/misc/adutux.c b/drivers/usb/misc/adutux.c
index 801324af9470..44f8b9225054 100644
--- a/drivers/usb/misc/adutux.c
+++ b/drivers/usb/misc/adutux.c
@@ -679,6 +679,7 @@ static const struct file_operations adu_fops = {
 	.write = adu_write,
 	.open = adu_open,
 	.release = adu_release,
+	.llseek = noop_llseek,
 };
 
 /*
diff --git a/drivers/usb/misc/idmouse.c b/drivers/usb/misc/idmouse.c
index a54c3cb804ce..c6184b4d1695 100644
--- a/drivers/usb/misc/idmouse.c
+++ b/drivers/usb/misc/idmouse.c
@@ -105,6 +105,7 @@ static const struct file_operations idmouse_fops = {
 	.read = idmouse_read,
 	.open = idmouse_open,
 	.release = idmouse_release,
+	.llseek = default_llseek,
 };
 
 /* class driver information */
diff --git a/drivers/usb/misc/iowarrior.c b/drivers/usb/misc/iowarrior.c
index bc88c79875a1..9b50db257019 100644
--- a/drivers/usb/misc/iowarrior.c
+++ b/drivers/usb/misc/iowarrior.c
@@ -730,6 +730,7 @@ static const struct file_operations iowarrior_fops = {
 	.open = iowarrior_open,
 	.release = iowarrior_release,
 	.poll = iowarrior_poll,
+	.llseek = noop_llseek,
 };
 
 static char *iowarrior_devnode(struct device *dev, mode_t *mode)
diff --git a/drivers/usb/misc/ldusb.c b/drivers/usb/misc/ldusb.c
index dd41d8710043..edffef642337 100644
--- a/drivers/usb/misc/ldusb.c
+++ b/drivers/usb/misc/ldusb.c
@@ -613,6 +613,7 @@ static const struct file_operations ld_usb_fops = {
 	.open =		ld_usb_open,
 	.release =	ld_usb_release,
 	.poll =		ld_usb_poll,
+	.llseek =	no_llseek,
 };
 
 /*
diff --git a/drivers/usb/misc/rio500.c b/drivers/usb/misc/rio500.c
index cc13ae61712a..4e23d3841b43 100644
--- a/drivers/usb/misc/rio500.c
+++ b/drivers/usb/misc/rio500.c
@@ -439,6 +439,7 @@ static const struct file_operations usb_rio_fops = {
 	.unlocked_ioctl = ioctl_rio,
 	.open =		open_rio,
 	.release =	close_rio,
+	.llseek =	noop_llseek,
 };
 
 static struct usb_class_driver usb_rio_class = {
diff --git a/drivers/usb/misc/usblcd.c b/drivers/usb/misc/usblcd.c
index d00dde19194c..51648154bb44 100644
--- a/drivers/usb/misc/usblcd.c
+++ b/drivers/usb/misc/usblcd.c
@@ -282,6 +282,7 @@ static const struct file_operations lcd_fops = {
         .open =         lcd_open,
 	.unlocked_ioctl = lcd_ioctl,
         .release =      lcd_release,
+        .llseek =	 noop_llseek,
 };
 
 /*
diff --git a/drivers/usb/usb-skeleton.c b/drivers/usb/usb-skeleton.c
index 552679b8dbd1..e24ce3123071 100644
--- a/drivers/usb/usb-skeleton.c
+++ b/drivers/usb/usb-skeleton.c
@@ -507,6 +507,7 @@ static const struct file_operations skel_fops = {
 	.open =		skel_open,
 	.release =	skel_release,
 	.flush =	skel_flush,
+	.llseek =	noop_llseek,
 };
 
 /*