linux-kernel - Re: [PATCH] pipefs unique inode numbers

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Date:	Tue, 30 Jan 2007 20:19:01 -0500
From:	Jeff Layton <jlayton@...hat.com>
To:	Bodo Eggert <7eggert@....de>
CC:	akpm@...l.org, Jeff Layton <jlayton@...hat.com>, dev@...ru,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	torvalds@...l.org
Subject: Re: [PATCH] pipefs unique inode numbers

Bodo Eggert wrote:
 > change pipefs to use a unique inode number equal to the memory
 > address unless it would be truncated.
 >
 > Signed-Off-By: Bodo Eggert <7eggert@....de>
 > ---
 > Tested on i386.
 >
 > --- 2.6.19/fs/pipe.c.ori	2007-01-30 22:02:46.000000000 +0100
 > +++ 2.6.19/fs/pipe.c	2007-01-30 23:22:27.000000000 +0100
 > @@ -864,6 +864,10 @@ static struct inode * get_pipe_inode(voi
 >  	inode->i_uid = current->fsuid;
 >  	inode->i_gid = current->fsgid;
 >  	inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
 > +	/* The address of *inode is unique, so we'll get an unique inode number.
 > +	 * Off cause this will not work for 32 bit inodes on 64 bit systems. */
 > +	if (sizeof(inode->i_ino) >= sizeof(struct inode*))
 > +		inode->i_ino = (unsigned int) inode;
 >
 >  	return inode;
 >

Also, that patch would break many 32-bit programs not compiled with large
offsets when run in compatibility mode on a 64-bit kernel. If they were to
do a stat on this inode, it would likely generate an EOVERFLOW error since
the pointer address would probably not fit in a 32 bit field.

That problem was the whole impetus for this set of patches.

-- Jeff
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