linux-ext4 - Re: Is EXT4_FITS_IN

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Message-ID: <20151105175941.GC2213@birch.djwong.org>
Date:	Thu, 5 Nov 2015 09:59:41 -0800
From:	"Darrick J. Wong" <darrick.wong@...cle.com>
To:	David Howells <dhowells@...hat.com>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: Is EXT4_FITS_IN_INODE() broken?

On Thu, Nov 05, 2015 at 05:18:57PM +0000, David Howells wrote:
> Is EXT4_FITS_IN_INODE() broken?  It makes use of i_extra_isize - which is an
> optional field and doesn't exist if the filesystem was made with "-I 128".
> 
> 	(gdb) p &((struct ext4_inode *)0)->i_extra_isize
> 	$2 = (__le16 *) 0x80 <irq_stack_union+128>
> 
> Should EXT4_FITS_IN_INODE():
> 
> 	#define EXT4_FITS_IN_INODE(ext4_inode, einode, field)	\
> 		((offsetof(typeof(*ext4_inode), field) +	\
> 		  sizeof((ext4_inode)->field))			\
> 		<= (EXT4_GOOD_OLD_INODE_SIZE +			\
> 		    (einode)->i_extra_isize))			\
> 
> be using EXT4_INODE_SIZE() and consulting the superblock instead?

In theory, all the callers should check EXT4_INODE_SIZE() beforehand...

...but that doesn't seem to be happening for the *INODE_[SG]ET_XTIME macros.
I think it's time to turn all those macros into proper static inline functions
and make them do the size checks rather than hoping we open-code it correctly.

(Also, the XTIME macros themselves are ugly.)

--D

> 
> David
> --
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