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Date: Mon, 19 Apr 2010 14:52:16 +0200
From: fweisbec@...il.com
To: Jan Blunck <jblunck@...e.de>
Cc: Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
Arnd Bergmann <arnd@...db.de>,
Thomas Gleixner <tglx@...utronix.de>,
Al Viro <viro@...IV.linux.org.uk>
Subject: Re: [GIT PULL] Preparation for BKL'ed ioctl removal
On Mon, Apr 19, 2010 at 02:30:03PM +0200, Jan Blunck wrote:
> On Fri, Apr 16, Frederic Weisbecker wrote:
>
> > 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@...db.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@...db.de>
> > Signed-off-by: Frederic Weisbecker <fweisbec@...il.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);
>
> Any specific reason why the default llseek() is in this patch?
>
> Jan
Because this comes along the same kind of bkl preparation work
we want to do. The goal is to isolate default_llseek and deprecated_ioctl
and only enable them if CONFIG_BKL.
Hence we want their declaration in smp_lock.h
That said it is probably not needed to get the default_llseek declaration
here for this release.
I'm going to make a v2 and resend the pull request. Thanks.
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