Re: [PATCH] fs: kill default_llseek

[Dave Anderson <anderson@redhat.com>]

----- 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@arndb.de>
> > 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@redhat.com>
> > 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?

Dave