On 12/29, Jonathan Corbet wrote:
>
> After pondering for a while, I couldn't come up with anything better than a
> global file->f_flags mutex. There's no point in bloating struct file with
> a mutex just for this purpose; it's hard to imagine that there will be any
> real contention for this lock.
Yes, this patch is simple and straightforward, but now we can't change
->f_flags in non-preempible context. And the global lock is not very
nice anyway.
Once again, can't we use O_LOCK_FLAGS bit? I agree, it is a bit ugly,
and I won't insist if you don't like is.
static inline int try_lock_f_flags(struct file *file)
{
return !test_and_set_bit(O_LOCK_FLAGS, file->f_flags);
}
static inline set_f_flags(struct file *file, unsigned int flags)
{
file->f_flags = flags & ~O_LOCK_FLAGS;
}
Now, nobody should change ->f_flags directly (except create/open
pathes. For example, ioctl_fionbio() should be changed:
if (try_lock_f_flags(filp)) {
if (on)
set_f_flags(filp, filp->f_flags | flag);
else
set_f_flags(filp, filp->f_flags & ~flag);
}
If try_lock_f_flags() fails we do nothing, as if the current owner of
O_LOCK_FLAGS changes ->f_flags after us.
What do you think?
> @@ -1116,6 +1116,7 @@ static int blkdev_open(struct inode * inode, struct
> file * filp)
> * binary needs it. We might want to drop this workaround
> * during an unstable branch.
> */
> + lock_file_flags();
> filp->f_flags |= O_LARGEFILE;
>
> if (filp->f_flags & O_NDELAY)
> @@ -1124,6 +1125,7 @@ static int blkdev_open(struct inode * inode, struct
> file * filp)
> filp->f_mode |= FMODE_EXCL;
> if ((filp->f_flags & O_ACCMODE) == 3)
> filp->f_mode |= FMODE_WRITE_IOCTL;
> + unlock_file_flags();
do we really need lock_file_flags() here?
> diff --git a/fs/pipe.c b/fs/pipe.c
> index 7aea8b8..23ae227 100644
> --- a/fs/pipe.c
> +++ b/fs/pipe.c
> @@ -945,7 +945,9 @@ struct file *create_write_pipe(int flags)
> goto err_dentry;
> f->f_mapping = inode->i_mapping;
>
> + lock_file_flags();
> f->f_flags = O_WRONLY | (flags & O_NONBLOCK);
> + unlock_file_flags();
> f->f_version = 0;
>
> return f;
> @@ -981,7 +983,9 @@ struct file *create_read_pipe(struct file *wrf, int flags)
> f->f_mapping = wrf->f_path.dentry->d_inode->i_mapping;
>
> f->f_pos = 0;
> + lock_file_flags();
> f->f_flags = O_RDONLY | (flags & O_NONBLOCK);
> + unlock_file_flags();
Ditto. Nobody can see this file yet, we can change ->f_flags lockless.
But please correct me if I am wrong, I know nothing about fs/.
Oleg.
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