On Sun, Dec 18, 2011 at 07:18:20AM -0700, Andreas Dilger wrote:
> On 2011-12-13, at 18:14, "Darrick J. Wong" <djwong@xxxxxxxxxx> wrote:
> > Provide a field in the block group descriptor to store inode bitmap checksum,
> > and some helper functions to calculate and verify it.
> > +int ext2fs_inode_bitmap_csum_verify(ext2_filsys fs, dgrp_t group,
> > + char *bitmap, int size)
> > +{
> > + struct ext4_group_desc *gdp = (struct ext4_group_desc *)
> > + ext2fs_group_desc(fs, fs->group_desc, group);
> > + __u32 provided, calculated;
> > +
> > + if (!EXT2_HAS_RO_COMPAT_FEATURE(fs->super,
> > + EXT4_FEATURE_RO_COMPAT_METADATA_CSUM))
> > + return 1;
> > + provided = gdp->bg_inode_bitmap_csum_lo;
> > + calculated = ext2fs_crc32c_le(~0, fs->super->s_uuid,
> > + sizeof(fs->super->s_uuid));
>
> It makes sense to precompute the uuid checksum and store it in the
> ext2_filsys struct so that it is accessible everywhere, like is done in the
> kernel.
I wonder how much that'll help compared to the IO overhead, but I suppose every
bit helps.
> > + calculated = ext2fs_crc32c_le(calculated, (unsigned char *)bitmap,
> > + size);
> > + if (fs->super->s_desc_size >= EXT4_BG_INODE_BITMAP_CSUM_HI_LOCATION)
> > + provided |= (__u32)gdp->bg_inode_bitmap_csum_hi << 16;
> > + else
> > + calculated &= 0xFFFF;
> > +
> > + return provided == calculated;
> > +}
> > +
> >
> > +++ b/lib/ext2fs/ext2_fs.h
> > @@ -191,6 +191,10 @@ struct ext4_group_desc
> > __u32 bg_reserved;
> > };
> >
> > +#define EXT4_BG_INODE_BITMAP_CSUM_HI_LOCATION \
> > + (offsetof(struct ext4_group_desc, bg_inode_bitmap_csum_hi) + \
> > + sizeof(__u16))
>
> It is a bit misleading to call this constant the "location" since it is
> actually the end of the csum_hi field. Either the sizeof(__u16) should be
> moved to the caller, or this should be renamed to
> EXT4_BG_INODE_BITMAP_CSUM_HI_END or similar.
Ok.
--D
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