On Thu, 2005-12-01 at 16:59 -0800, Mingming Cao wrote:
> Badari Pulavarty wrote:
> > Hi,
> >
> > Here is the patch to support ext3 getblocks() for non allocation
> > cases. (for reads & re-writes). This is useful with DIO reads,
> > DIO re-writes and to go with Christoph's getblocks() for readpages()
> > work.
> >
> > Mingming is working on adding multiblock allocation support using
> > reservation (which can be incrementally added later).
> >
> > Comments ?
> >
>
> My ext3 multiple block allocation patch posted a while ago
> includes the multiple blocks map as well. Looks mostly the same way you
> did here, but I like the way that how the # of mapped(or allocated)
> blocks are returned.
>
> My plan is to break the whole ext3 multiple block allocation(also does
> map) patch into small patches, and re-send soon.
Cool. Can you handle this one too then ?
>
> > @@ -681,9 +683,10 @@ ext3_get_block_handle(handle_t *handle,
> > Indirect *partial;
> > unsigned long goal;
> > int left;
> > - int boundary = 0;
> > - const int depth = ext3_block_to_path(inode, iblock, offsets, &boundary);
> > + int blks_boundary = 0;
> > + const int depth = ext3_block_to_path(inode, iblock, offsets, &blks_boundary);
> > struct ext3_inode_info *ei = EXT3_I(inode);
> > + int count = 1;
> >
> > J_ASSERT(handle != NULL || create == 0);
> >
> > @@ -694,7 +697,18 @@ ext3_get_block_handle(handle_t *handle,
> >
> > /* Simplest case - block found, no allocation needed */
> > if (!partial) {
> > + unsigned long first_block = le32_to_cpu(chain[depth-1].key);
> > +
> > clear_buffer_new(bh_result);
> > +
> > + /*
> > + * Find all the contiguous blocks and return at once.
> > + */
> > + while (count < max_blocks && count <= blks_boundary &&
> > + (le32_to_cpu(*(chain[depth-1].p+count)) ==
> > + (first_block + count))) {
> > + count++;
> > + }
> > goto got_it;
> > }
> >
> Here we need to be careful about the branch we just read, since we are
> looking up multiple blocks (they are on the same branch) at the same
> time, it is possible that during the look up, another threads is
> trucating the same branch we are trying to map. Before since we are
> doing only one look up, a simple verify_chain() should be safe.
>
> The simple way is, for the non-allocation case, take the truncate_sem
> before the ext3_get_branch, like for the allocation-case, even for the
> simple case -- but that probably will slow down the non-allocation,
> probably a bad option. But we could re-check(calling
> verify_chain())inside the while loop.
I don't think we can slowdown non-allocation read case, may be re-check
is a better idea ?
Thanks,
Badari
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