On Mon, Jun 02, 2008 at 06:02:21PM +0800, Shen Feng wrote:
>
>
> Theodore Tso Wrote:
> > On Thu, May 15, 2008 at 12:17:11AM +0530, Aneesh Kumar K.V wrote:
> >> @@ -3134,8 +3135,7 @@ static void ext4_mb_use_inode_pa(struct ext4_allocation_context *ac,
> >> static void ext4_mb_use_group_pa(struct ext4_allocation_context *ac,
> >> struct ext4_prealloc_space *pa)
> >> {
> >> - unsigned len = ac->ac_o_ex.fe_len;
> >> -
> >> + unsigned int len = ac->ac_o_ex.fe_len;
> >> ext4_get_group_no_and_offset(ac->ac_sb, pa->pa_pstart,
> >> &ac->ac_b_ex.fe_group,
> >> &ac->ac_b_ex.fe_start);
> >> --
> >
> > This change had nothing to do with fixing the use of unitialized data,
> > but when I started looking more closely, it raised a potential signed
> > vs. unsigned issue: ac_o_ex is a struct ext4_free_extent, and fe_len
> > is an int.
> >
> > So here we are assigning an int to an unsigned int. Later, len is
> > assigned to ac_b_ex.len, which means assigning an unsigned int to an
> > int. In other places, fe_len (an int) is compared against pa_free
> > (which is an unsigned short), and fe_len gets assined to pa_free, once
> > again mixing signed and unsigned.
> >
> > Can someone who is really familiar with this code check this out? I
> > think the following pseudo-patch to mballoc.h might be in order:
> >
> > struct ext4_free_extent {
> > ext4_lblk_t fe_logical;
> > ext4_grpblk_t fe_start;
> > ext4_group_t fe_group;
> > - int fe_len;
> > + unsigned int fe_len;
> > };
> >
>
> I'm studying the ext4 code these days.
> The data types always confuse me.
>
> The length of a ext4_extent ee_len is define as unsigned short.
>
> struct ext4_extent {
> __le32 ee_block; /* first logical block extent covers */
> __le16 ee_len; /* number of blocks covered by extent */
> __le16 ee_start_hi; /* high 16 bits of physical block */
> __le32 ee_start_lo; /* low 32 bits of physical block */
> };
>
> So I think fe_len should also be defined as unsigned short.
> Is that right?
Extents and each prealloc space have at max 2**16 blocks. So the length
of both should be unsigned short. With respect to ext4_free_extent we
use fe_len to store the number of blocks requested for allocation.
( ext4_mb_initialize_context )
The allocated extent will definitely have <= 2**16. But the requested
number of blocks may not.
-aneesh
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
