2021-05-10 06:48:10

by Gao Xiang

Subject: [PATCH] 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/[email protected]
Fixes: cec6e93beadf ("erofs: support parsing big pcluster compress indexes")
Signed-off-by: Gao Xiang <[email protected]>
---
fs/erofs/zmap.c | 21 +++++++++++++++++++--
1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/fs/erofs/zmap.c b/fs/erofs/zmap.c
index e62d813756f2..efaf32596b97 100644
--- a/fs/erofs/zmap.c
+++ b/fs/erofs/zmap.c
@@ -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;
--
2.20.1

2021-05-13 06:56:42

by Chao Yu

Subject: Re: [PATCH] erofs: fix 1 lcluster-sized pcluster for big pcluster

On 2021/5/10 14:47, Gao Xiang wrote:
> 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/[email protected]
> Fixes: cec6e93beadf ("erofs: support parsing big pcluster compress indexes")
> Signed-off-by: Gao Xiang <[email protected]>

Reviewed-by: Chao Yu <[email protected]>

Thanks,