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Date: Fri, 2 Sep 2011 11:43:32 -0700 From: "Darrick J. Wong" <djwong@...ibm.com> To: Andreas Dilger <adilger.kernel@...ger.ca> Cc: Theodore Tso <tytso@....edu>, Sunil Mushran <sunil.mushran@...cle.com>, Amir Goldstein <amir73il@...il.com>, linux-kernel <linux-kernel@...r.kernel.org>, Andi Kleen <andi@...stfloor.org>, Mingming Cao <cmm@...ibm.com>, Joel Becker <jlbec@...lplan.org>, linux-fsdevel <linux-fsdevel@...r.kernel.org>, linux-ext4@...r.kernel.org, Coly Li <colyli@...il.com> Subject: Re: [PATCH 13/16] ext4: Calculate and verify checksums of extended attribute blocks On Thu, Sep 01, 2011 at 01:42:26AM -0600, Andreas Dilger wrote: > On 2011-08-31, at 6:32 PM, Darrick J. Wong wrote: > > Calculate and verify the checksums of extended attribute blocks. This only > > applies to separate EA blocks that are pointed to by inode->i_file_acl (i.e. > > external EA blocks); the checksum lives in the EA header. > > > > diff --git a/fs/ext4/xattr.h b/fs/ext4/xattr.h > > index 25b7387..b2b20af 100644 > > --- a/fs/ext4/xattr.h > > +++ b/fs/ext4/xattr.h > > @@ -27,7 +27,8 @@ struct ext4_xattr_header { > > __le32 h_refcount; /* reference count */ > > __le32 h_blocks; /* number of disk blocks used */ > > __le32 h_hash; /* hash value of all attributes */ > > - __u32 h_reserved[4]; /* zero right now */ > > + __le32 h_checksum; /* crc32c(uuid+inum+xattrblock) */ > > This comment is incorrect - the inum cannot be part of the checksum if > the block is shared. That said, I wouldn't object if the checksum DID > include the inum if the block was not shared (h_refcount == 1). Since > the h_refcount needs to be modified and the checksum recomputed if other > inodes share this block, this doesn't impose any extra overhead. Oops, I guess I was typing too fast. "inum" should be "ea_block_num". Though I suspect that in the common case files don't share EA blocks, so we could do inum when refcount==1. --D > > Cheers, Andreas > -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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