linux-kernel - Re: [PATCH] (resend) reuse xxx_fifo_fops for xxx_pipe

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Date:	Tue, 1 Jul 2008 12:03:50 +0200
From:	Denys Vlasenko <vda.linux@...glemail.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Al Viro <viro@...iv.linux.org.uk>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] (resend) reuse xxx_fifo_fops for xxx_pipe_fops

On Tuesday 01 July 2008 09:32, Andrew Morton wrote:
> > I noticed that read/write/rdwr_pipe_fops are (1) const and
> > (2) exactly identical to xxx_fifo_fops, which are also const.
> > 
> > Attached patch #defines xxx_pipe_fops as aliases to xxx_fifo_fops.
> > Size difference:
> > 
> > # size linux-2.6.25-rc6*/*/pipe.o
> >    text    data     bss     dec     hex filename
> >    6534     144       0    6678    1a16 linux-2.6.25-rc6/fs/pipe.o
> >    5862     144       0    6006    1776 linux-2.6.25-rc6-pt/fs/pipe.o
> > 
> > Run-tested on 2.6.26-rc8. Please apply.
> > 
> > Signed-off-by: Denys Vlasenko <vda.linux@...glemail.com>
> 
> <argh, an attachment.  save-as, read, edit..>

Let's see how KMail will cope with inline cut-n-paste...

> > -static const struct file_operations rdwr_pipe_fops = {
> > -	.llseek		= no_llseek,
> > -	.read		= do_sync_read,
> > -	.aio_read	= pipe_read,
> > -	.write		= do_sync_write,
> > -	.aio_write	= pipe_write,
> > -	.poll		= pipe_poll,
> > -	.unlocked_ioctl	= pipe_ioctl,
> > -	.open		= pipe_rdwr_open,
> > -	.release	= pipe_rdwr_release,
> > -	.fasync		= pipe_rdwr_fasync,
> > -};
> > +#define read_pipe_fops  read_fifo_fops
> > +#define write_pipe_fops write_fifo_fops
> > +#define rdwr_pipe_fops  rdwr_fifo_fops
> 
> Well OK.  But there's a risk that someone will go and modify
> read_fifo_fops without realising that they're also modifying
> read_pipe_fops.

Yes, it is possible.

> So it'd be better to rename read_fifo_fops to (say) shared_read_fops
> then do
> 
> #define read_pipe_fops shared_read_fops
> #define read_fifo_fops shared_read_fops

I think since XXX_pipe_fops are only used in this file,
just explaining this in the comment would be enough.

Please take a look at the version below.

Signed-off-by: Denys Vlasenko <vda.linux@...glemail.com>
--
vda


--- linux-2.6.26-rc8/fs/pipe.c.org	Tue Jul  1 11:52:28 2008
+++ linux-2.6.26-rc8/fs/pipe.c	Tue Jul  1 11:58:23 2008
@@ -777,6 +777,8 @@
 /*
  * The file_operations structs are not static because they
  * are also used in linux/fs/fifo.c to do operations on FIFOs.
+ *
+ * Pipes reuse fifos' file_operations structs.
  */
 const struct file_operations read_fifo_fops = {
 	.llseek		= no_llseek,
@@ -815,43 +817,6 @@
 	.fasync		= pipe_rdwr_fasync,
 };
 
-static const struct file_operations read_pipe_fops = {
-	.llseek		= no_llseek,
-	.read		= do_sync_read,
-	.aio_read	= pipe_read,
-	.write		= bad_pipe_w,
-	.poll		= pipe_poll,
-	.unlocked_ioctl	= pipe_ioctl,
-	.open		= pipe_read_open,
-	.release	= pipe_read_release,
-	.fasync		= pipe_read_fasync,
-};
-
-static const struct file_operations write_pipe_fops = {
-	.llseek		= no_llseek,
-	.read		= bad_pipe_r,
-	.write		= do_sync_write,
-	.aio_write	= pipe_write,
-	.poll		= pipe_poll,
-	.unlocked_ioctl	= pipe_ioctl,
-	.open		= pipe_write_open,
-	.release	= pipe_write_release,
-	.fasync		= pipe_write_fasync,
-};
-
-static const struct file_operations rdwr_pipe_fops = {
-	.llseek		= no_llseek,
-	.read		= do_sync_read,
-	.aio_read	= pipe_read,
-	.write		= do_sync_write,
-	.aio_write	= pipe_write,
-	.poll		= pipe_poll,
-	.unlocked_ioctl	= pipe_ioctl,
-	.open		= pipe_rdwr_open,
-	.release	= pipe_rdwr_release,
-	.fasync		= pipe_rdwr_fasync,
-};
-
 struct pipe_inode_info * alloc_pipe_info(struct inode *inode)
 {
 	struct pipe_inode_info *pipe;
@@ -927,7 +892,7 @@
 	inode->i_pipe = pipe;
 
 	pipe->readers = pipe->writers = 1;
-	inode->i_fop = &rdwr_pipe_fops;
+	inode->i_fop = &rdwr_fifo_fops;
 
 	/*
 	 * Mark the inode dirty from the very beginning,
@@ -978,7 +943,7 @@
 	d_instantiate(dentry, inode);
 
 	err = -ENFILE;
-	f = alloc_file(pipe_mnt, dentry, FMODE_WRITE, &write_pipe_fops);
+	f = alloc_file(pipe_mnt, dentry, FMODE_WRITE, &write_fifo_fops);
 	if (!f)
 		goto err_dentry;
 	f->f_mapping = inode->i_mapping;
@@ -1021,7 +986,7 @@
 
 	f->f_pos = 0;
 	f->f_flags = O_RDONLY;
-	f->f_op = &read_pipe_fops;
+	f->f_op = &read_fifo_fops;
 	f->f_mode = FMODE_READ;
 	f->f_version = 0;
 
--
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