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erofs: fix 1 lcluster-sized pcluster for big pcluster 

If the 1st NONHEAD lcluster of a pcluster isn't CBLKCNT lcluster type
rather than a HEAD or PLAIN type instead, which means its pclustersize
_must_ be 1 lcluster (since its uncompressed size < 2 lclusters),
as illustrated below:

       HEAD     HEAD / PLAIN    lcluster type
   ____________ ____________
  |_:__________|_________:__|   file data (uncompressed)
   .                .
  .____________.
  |____________|                pcluster data (compressed)

Such on-disk case was explained before [1] but missed to be handled
properly in the runtime implementation.

It can be observed if manually generating 1 lcluster-sized pcluster
with 2 lclusters (thus CBLKCNT doesn't exist.) Let's fix it now.

[1] https://lore.kernel.org/r/20210407043927.10623-1-xiang@kernel.org

Link: https://lore.kernel.org/r/20210510064715.29123-1-xiang@kernel.org
Fixes: cec6e93bea ("erofs: support parsing big pcluster compress indexes")
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <xiang@kernel.org>
This commit is contained in:
Gao Xiang 2021-05-10 14:47:15 +08:00
parent 46f2e04484
commit 0852b6ca94
1 changed files with 19 additions and 2 deletions
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21
fs/erofs/zmap.c
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@ -450,14 +450,31 @@ static int z_erofs_get_extent_compressedlen(struct z_erofs_maprecorder *m,
lcn = m->lcn + 1;
if (m->compressedlcs)
goto out;
if (lcn == initial_lcn)
goto err_bonus_cblkcnt;
err = z_erofs_load_cluster_from_disk(m, lcn);
if (err)
return err;
/*
* If the 1st NONHEAD lcluster has already been handled initially w/o
* valid compressedlcs, which means at least it mustn't be CBLKCNT, or
* an internal implemenatation error is detected.
*
* The following code can also handle it properly anyway, but let's
* BUG_ON in the debugging mode only for developers to notice that.
*/
DBG_BUGON(lcn == initial_lcn &&
m->type == Z_EROFS_VLE_CLUSTER_TYPE_NONHEAD);
switch (m->type) {
case Z_EROFS_VLE_CLUSTER_TYPE_PLAIN:
case Z_EROFS_VLE_CLUSTER_TYPE_HEAD:
/*
* if the 1st NONHEAD lcluster is actually PLAIN or HEAD type
* rather than CBLKCNT, it's a 1 lcluster-sized pcluster.
*/
m->compressedlcs = 1;
break;
case Z_EROFS_VLE_CLUSTER_TYPE_NONHEAD:
if (m->delta[0] != 1)
goto err_bonus_cblkcnt;