Re: [PATCH] fs: kill default_llseek

[Josef Bacik]

On 05/09/2011 02:30 PM, Dave Anderson wrote:
> ----- Original Message -----
> > On 05/09/2011 02:03 PM, Dave Anderson wrote:
> > > On Thursday 05 May 2011 16:27:57 Josef Bacik wrote:
> > > > Looking at this llseek stuff I noticed that default_llseek is the
> > > > exact same as
> > > > generic_file_llseek, so kill default_llseek. I patched this using
> > > > spatch with
> > > > just a simple
> > > >
> > > > @@
> > > > @@
> > > >
> > > > - default_llseek
> > > > + generic_file_llseek
> > >
> > > ...
> > >
> > > > diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
> > > > index d245cb2..6f37c39 100644
> > > > --- a/fs/proc/kcore.c
> > > > +++ b/fs/proc/kcore.c
> > > > @@ -558,7 +558,7 @@ static int open_kcore(struct inode *inode,
> > > > struct file *filp)
> > > >    static const struct file_operations proc_kcore_operations = {
> > > >    	.read = read_kcore,
> > > >    	.open = open_kcore,
> > > > - .llseek = default_llseek,
> > > > + .llseek = generic_file_llseek,
> > > >    };
> > >
> > > > diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c
> > > > index 74802bc5..0cafd9e 100644
> > > > --- a/fs/proc/vmcore.c
> > > > +++ b/fs/proc/vmcore.c
> > > > @@ -163,7 +163,7 @@ static ssize_t read_vmcore(struct file *file,
> > > > char __user *buffer,
> > > >
> > > >    static const struct file_operations proc_vmcore_operations = {
> > > >    	.read = read_vmcore,
> > > > - .llseek = default_llseek,
> > > > + .llseek = generic_file_llseek,
> > > >    };
> > >
> > > Both /proc/kcore and /proc/vmcore currently require
> > > default_llseek().
> > > They were both changed to use generic_file_llseek(), but then
> > > subsequently
> > > reverted back to default_llseek():
> > >
> > > commit c227e69028473c7c7994a9b0a2cc0034f3f7e0fe
> > > Author: Arnd Bergmann<arnd@xxxxxxxx>
> > > Date: Wed Sep 22 13:04:54 2010 -0700
> > >
> > >       /proc/vmcore: fix seeking
> > >
> > >       Commit 73296bc611 ("procfs: Use generic_file_llseek in
> > >       /proc/vmcore")
> > >       broke seeking on /proc/vmcore. This changes it back to use
> > >       default_llseek
> > >       in order to restore the original behaviour.
> > >       ...
> > >
> > >
> > > commit ceff1a770933e2ca2bf995b453dade4ec47a9878
> > > Author: Dave Anderson<anderson@xxxxxxxxxx>
> > > Date: Wed Jan 12 17:00:36 2011 -0800
> > >
> > >       /proc/kcore: fix seeking
> > >
> > >       Commit 34aacb2920 ("procfs: Use generic_file_llseek in
> > >       /proc/kcore") broke
> > >       seeking on /proc/kcore. This changes it back to use
> > >       default_llseek in
> > >       order to restore the original behavior.
> > >       ...
> >
> > How is it getting s_maxbytes set to 0? I'm looking everywhere and I
> > can't see how that can happen. It seems that anybody using sget should
> > be getting it set to MAX_NONLFS so they should all be ok. I'm looking
> > at proc in particular and it doesn't do anything special, so it should
> > be ok. (Obviously it wasn't, I'm just trying to understand how we're
> > getting s_maxbytes == 0 so we can fix that and kill default_llseek).
> > Thanks,
> >
> > Josef
>
> Well, in the case of /proc/kcore, it was set to MAX_NON_LFS (2GB-1)
> which is too small because the file offset values in the /proc/kcore
> PT_LOAD segments may exceed or start beyond that offset value.
>
> I guessing the same thing was seen with /proc/vmcore, even
> though Arnd's commit message implies that it was 0?

Ah yeah I guess that's it.  Alright I'll think of something else.  Thanks,

Josef
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