linux-kernel - Re: [PATCH v3 5/7] fs: remove no

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Date:   Thu, 30 Jun 2022 15:50:41 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Nikolay Borisov <n.borisov.lkml@...il.com>
Cc:     linux-kernel@...r.kernel.org, viro@...iv.linux.org.uk
Subject: Re: [PATCH v3 5/7] fs: remove no_llseek

Hi Nikolay,

On Thu, Jun 30, 2022 at 09:45:04AM +0300, Nikolay Borisov wrote:
> 
> 
> On 29.06.22 г. 16:07 ч., Jason A. Donenfeld wrote:
> > Now that all callers of ->llseek are going through vfs_llseek(), we
> > don't gain anything by keeping no_llseek around. Nothing compares it or
> > calls it.
> > 
> > Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
> > ---
> >   fs/read_write.c    | 17 +++--------------
> >   include/linux/fs.h |  1 -
> >   2 files changed, 3 insertions(+), 15 deletions(-)
> > 
> > diff --git a/fs/read_write.c b/fs/read_write.c
> > index b1b1cdfee9d3..69cd8d72d91e 100644
> > --- a/fs/read_write.c
> > +++ b/fs/read_write.c
> > @@ -227,12 +227,6 @@ loff_t noop_llseek(struct file *file, loff_t offset, int whence)
> >   }
> >   EXPORT_SYMBOL(noop_llseek);
> >   
> > -loff_t no_llseek(struct file *file, loff_t offset, int whence)
> > -{
> > -	return -ESPIPE;
> > -}
> > -EXPORT_SYMBOL(no_llseek);
> > -
> >   loff_t default_llseek(struct file *file, loff_t offset, int whence)
> >   {
> >   	struct inode *inode = file_inode(file);
> > @@ -290,14 +284,9 @@ EXPORT_SYMBOL(default_llseek);
> >   
> >   loff_t vfs_llseek(struct file *file, loff_t offset, int whence)
> >   {
> > -	loff_t (*fn)(struct file *, loff_t, int);
> > -
> > -	fn = no_llseek;
> > -	if (file->f_mode & FMODE_LSEEK) {
> > -		if (file->f_op->llseek)
> > -			fn = file->f_op->llseek;
> > -	}
> > -	return fn(file, offset, whence);
> > +	if (!(file->f_mode & FMODE_LSEEK) || !file->f_op->llseek)
> 
> Is it not sufficient here to just check for the presence of FMODE_LSEEK? 
> NULL  llseek shall result in FMODE_LSEEK not being set when the file is 
> opened?

Yes, that's probably fine. I did this out of an abundance of caution,
but I have a feeling Al might agree with you that useless is useless. I
can send a v4 changing that.

Al, what do you think?

Jason