[GIT PULL] Preparation for BKL'ed ioctl removal

* [GIT PULL] Preparation for BKL'ed ioctl removal
@ 2010-04-16  3:56 Frederic Weisbecker
  2010-04-22  0:48 ` [GIT PULL v2] " Frederic Weisbecker
  0 siblings, 1 reply; 41+ messages in thread
From: Frederic Weisbecker @ 2010-04-16  3:56 UTC (permalink / raw)
  To: Linus Torvalds
  Cc: LKML, Frederic Weisbecker, Arnd Bergmann, Thomas Gleixner,
	Al Viro, Jan Blunck, Ingo Molnar

Linus,

In order to stop the bkl contagion in ioctl and push the
bkl from Vfs to the drivers that don't implement a proper
unlock_ioctl, this patch proposes to add a new "locked_ioctl"
field in struct file_operation.

This field is never called from vfs and requires to assign a
new "deprecated_ioctl" helper to the unlocked_ioctl field.
This deprecated_ioctl() helper then calls the locked_ioctl()
callback with the bkl held.

The point of doing this is to change every users of fops::ioctl
to the new scheme. Once there is no more users of the ioctl field,
we'll then be able to remove it.

Also this change brings a new config BKL which is always
enabled for now. Every drivers that use the bkl through
explicit lock_kernel() calls or by using deprecated_ioctl()
will have to select CONFIG_BKL.

Once we get no more uses of the bkl from the core features but
only on individual drivers, config BKL can be turned off
by default and selected by those drivers if needed, relegating
the bkl as an obsolete library for poor old drivers.

And given the work happening currently (tty mutex, vfs pushdowns,
procfs bkl removal, llseek janitorials, etc...), this may happen
sooner than was expected.

Now the point of having this patch in 2.6.34 is to turn
the old ioctl implementations to the new scheme in a set
of patches that relevant maintainers can apply to their
tree (or apply by ourself for unmaintained areas) for .35
Otherwise we would need to queue everything in a single
tree that may bring conflicts in the next merge window.

This single patch has very few chances to bring any regressions.

Please pull the bkl/ioctl branch that can be found at:

git://git.kernel.org/pub/scm/linux/kernel/git/frederic/random-tracing.git
	bkl/ioctl

Thanks,
	Frederic
---

Arnd Bergmann (1):
      vfs: Introduce CONFIG_BKL and deprecated_ioctl


 fs/ioctl.c               |   22 ++++++++++++++++++++++
 include/linux/fs.h       |    3 +++
 include/linux/smp_lock.h |    4 ++++
 kernel/Kconfig.locks     |   10 ++++++++++
 4 files changed, 39 insertions(+), 0 deletions(-)

---
commit 588a2267f7b2919ae73380e0932cc6a202787036
Author: Arnd Bergmann <arnd@arndb.de>
Date:   Thu Apr 1 14:42:38 2010 +0200

    vfs: Introduce CONFIG_BKL and deprecated_ioctl
    
    This is a preparation for the removal of the big kernel lock that
    introduces new interfaces for device drivers still using it.
    
    We can start marking those device drivers as 'depends on CONFIG_BKL'
    now, and make that symbol optional later, when the point has come
    at which we are able to build a kernel without the BKL.
    
    Similarly, device drivers that currently make use of the implicit
    BKL locking around the ioctl function can now get annotated by
    changing
    
    	.ioctl = foo_ioctl,
    
    to
    
    	.locked_ioctl = foo_ioctl,
    	.unlocked_ioctl = deprecated_ioctl,
    
    As soon as no driver remains using the old ioctl callback, it can
    get removed.
    
    [fweisbec: move config bkl from Kconfig.debug to Kconfig.locks,
    rename default_ioctl to deprecated_ioctl]
    
    Signed-off-by: Arnd Bergmann <arnd@arndb.de>
    Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>

diff --git a/fs/ioctl.c b/fs/ioctl.c
index 6c75110..e6d6a75 100644
--- a/fs/ioctl.c
+++ b/fs/ioctl.c
@@ -58,6 +58,28 @@ static long vfs_ioctl(struct file *filp, unsigned int cmd,
 	return error;
 }
 
+#ifdef CONFIG_BKL
+/*
+ * deprecated_ioctl - call locked_ioctl with BKL held
+ *
+ * Setting only the ioctl operation but not unlocked_ioctl will become
+ * invalid in the future, all drivers that are not converted to unlocked_ioctl
+ * should set .unlocked_ioctl = deprecated_ioctl now.
+ */
+long deprecated_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
+{
+	int error = -ENOTTY;
+	if (filp->f_op->locked_ioctl) {
+		lock_kernel();
+		error = filp->f_op->locked_ioctl(filp->f_path.dentry->d_inode,
+						 filp, cmd, arg);
+		unlock_kernel();
+	}
+	return error;
+}
+EXPORT_SYMBOL_GPL(default_ioctl);
+#endif
+
 static int ioctl_fibmap(struct file *filp, int __user *p)
 {
 	struct address_space *mapping = filp->f_mapping;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 39d57bc..6b65b26 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1492,6 +1492,9 @@ struct file_operations {
 	int (*readdir) (struct file *, void *, filldir_t);
 	unsigned int (*poll) (struct file *, struct poll_table_struct *);
 	int (*ioctl) (struct inode *, struct file *, unsigned int, unsigned long);
+#ifdef CONFIG_BKL
+	int (*locked_ioctl) (struct inode *, struct file *, unsigned int, unsigned long);
+#endif
 	long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
 	long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
 	int (*mmap) (struct file *, struct vm_area_struct *);
diff --git a/include/linux/smp_lock.h b/include/linux/smp_lock.h
index 2ea1dd1..c8693e1 100644
--- a/include/linux/smp_lock.h
+++ b/include/linux/smp_lock.h
@@ -62,4 +62,8 @@ static inline void cycle_kernel_lock(void)
 #define kernel_locked()				1
 
 #endif /* CONFIG_LOCK_KERNEL */
+
+loff_t default_llseek(struct file *file, loff_t offset, int origin);
+long deprecated_ioctl(struct file *filp, unsigned int cmd, unsigned long arg);
+
 #endif /* __LINUX_SMPLOCK_H */
diff --git a/kernel/Kconfig.locks b/kernel/Kconfig.locks
index 88c92fb..9a80413 100644
--- a/kernel/Kconfig.locks
+++ b/kernel/Kconfig.locks
@@ -200,3 +200,13 @@ config INLINE_WRITE_UNLOCK_IRQRESTORE
 
 config MUTEX_SPIN_ON_OWNER
 	def_bool SMP && !DEBUG_MUTEXES && !HAVE_DEFAULT_NO_SPIN_MUTEXES
+
+config BKL
+	def_bool y
+	help
+	  This is the traditional lock that is used in old code instead
+	  of proper locking. All drivers that use the BKL should depend
+	  on this symbol.
+	  This configuration option will become user-selectable in the
+	  future, as soon as it is possible to build a kernel without
+	  it.

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