linux-ext4 - Re: [ext4:dev 37/63] fs/ext4/inline.c:268:19: error: 'empty_zero

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Message-ID: <20121211051205.GA23653@thunk.org>
Date:	Tue, 11 Dec 2012 00:12:05 -0500
From:	Theodore Ts'o <tytso@....edu>
To:	Tao Ma <tm@....ma>
Cc:	kbuild test robot <fengguang.wu@...el.com>,
	Tao Ma <boyu.mt@...bao.com>, linux-ext4@...r.kernel.org
Subject: Re: [ext4:dev 37/63] fs/ext4/inline.c:268:19: error:
 'empty_zero_page' undeclared

On Tue, Dec 11, 2012 at 10:25:37AM +0800, Tao Ma wrote:
> uh, in sparc, we don't have empty_zero_page? I just want to create an
> inline data file without allocating a buffer with the specified length.
> So maybe I have to do the kzalloc thing then. :(

Yeah, sparc64 apparently doesn't have empty_zero_page.  All
architectures have ZERO_PAGE(0), which is what the DIO code uses, but
you can't count on it being mapped.

What we could do instead is pass in a value of "(void *) -1", and then
in ext4_xattr_set_entry(), if i->value is -1, use memset to zero out
the value instead of memcpy.  This will be safe for all architectures,
since we already use casts of negative values for ERR_PTR.

In fact, we could just use "i.value = ERR_PTR(-1)" and
"IS_ERR_VALUE(i->value)", but it would be clearer to explicitly define
EXT4_ZERO_XATTR_VALUE to be "((void *) -1)", and use that to indicate
that ext4_xattr_set_entry() should zero out the page in question.

     			    	   	    	- Ted
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