From: Jan Kara Subject: Re: [PATCH] ext4: Return the length of a hole from get_block Date: Mon, 13 Jul 2015 17:16:10 +0200 Message-ID: <20150713151610.GC17075@quack.suse.cz> References: <1435936511-17705-1-git-send-email-matthew.r.wilcox@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Theodore Ts'o , Andreas Dilger , linux-ext4@vger.kernel.org, Matthew Wilcox To: Matthew Wilcox Return-path: Received: from cantor2.suse.de ([195.135.220.15]:48616 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751168AbbGMPQM (ORCPT ); Mon, 13 Jul 2015 11:16:12 -0400 Content-Disposition: inline In-Reply-To: <1435936511-17705-1-git-send-email-matthew.r.wilcox@intel.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Fri 03-07-15 11:15:11, Matthew Wilcox wrote: > From: Matthew Wilcox > > Currently, if ext4's get_block encounters a hole, it does not modify the > buffer_head. That's fine for many callers, but for DAX, it's useful to > know how large the hole is. XFS already returns the length of the hole, > so this improvement should not confuse any callers. > > Signed-off-by: Matthew Wilcox So I'm somewhat wondering: What is the reason of BH_Uptodate flag being set? I can see the XFS sets it in some cases as well but the use of the flag isn't really clear to me... Honza > --- > fs/ext4/ext4.h | 6 ++++-- > fs/ext4/inode.c | 6 +++++- > 2 files changed, 9 insertions(+), 3 deletions(-) > > diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h > index 9a83f14..7b7c097 100644 > --- a/fs/ext4/ext4.h > +++ b/fs/ext4/ext4.h > @@ -154,12 +154,14 @@ struct ext4_allocation_request { > * well as to store the information returned by ext4_map_blocks(). It > * takes less room on the stack than a struct buffer_head. > */ > +#define EXT4_MAP_UPTODATE (1 << BH_Uptodate) > #define EXT4_MAP_NEW (1 << BH_New) > #define EXT4_MAP_MAPPED (1 << BH_Mapped) > #define EXT4_MAP_UNWRITTEN (1 << BH_Unwritten) > #define EXT4_MAP_BOUNDARY (1 << BH_Boundary) > -#define EXT4_MAP_FLAGS (EXT4_MAP_NEW | EXT4_MAP_MAPPED |\ > - EXT4_MAP_UNWRITTEN | EXT4_MAP_BOUNDARY) > +#define EXT4_MAP_FLAGS (EXT4_MAP_UPTODATE | EXT4_MAP_NEW | \ > + EXT4_MAP_MAPPED | EXT4_MAP_UNWRITTEN | \ > + EXT4_MAP_BOUNDARY) > > struct ext4_map_blocks { > ext4_fsblk_t m_pblk; > diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c > index 9b46f6f..0fc49ac 100644 > --- a/fs/ext4/inode.c > +++ b/fs/ext4/inode.c > @@ -494,7 +494,11 @@ int ext4_map_blocks(handle_t *handle, struct inode *inode, > retval = map->m_len; > map->m_len = retval; > } else if (ext4_es_is_delayed(&es) || ext4_es_is_hole(&es)) { > - retval = 0; > + map->m_flags |= EXT4_MAP_UPTODATE; > + retval = es.es_len - (map->m_lblk - es.es_lblk); > + if (retval > map->m_len) > + retval = map->m_len; > + map->m_len = retval; > } else { > BUG_ON(1); > } > -- > 2.1.4 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-ext4" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- Jan Kara SUSE Labs, CR