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fs: ext4: Problem with ext4load and sparse files

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Hi,

when I try to load a sparse file via ext4load, I am getting the error message
'invalid extent'

After a deeper look in the code, it seems to be an issue in the function ext4fs_get_extent_block in fs/ext4/ext4_common.c:

The file starts with 1k of zeros. The blocksize is 1024. So the first extend block contains the following information:

eh_entries: 1
eh_depth: 1
ei_block 1

When the upper layer (ext4fs_read_file) asks for fileblock 0, we are running in the 'invalid extent' error message.
For me it seems, that the code is not prepared for handling a sparse block at the beginning of the file. The following change, solved my problem:

I am really not an expert in ext4 filesystems. Can somebody please have a look at this issue and give me a feedback, if I am totally wrong or not?
This commit is contained in:
Gero Schumacher 2019-02-26 15:45:22 +00:00 committed by Tom Rini
parent ef79284e7a
commit 1c48fda3e5
1 changed files with 6 additions and 2 deletions
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8
fs/ext4/ext4_common.c
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@ -1547,8 +1547,12 @@ static struct ext4_extent_header *ext4fs_get_extent_block
break;
} while (fileblock >= le32_to_cpu(index[i].ei_block));
if (--i < 0)
return NULL;
/*
* If first logical block number is higher than requested fileblock,
* it is a sparse file. This is handled on upper layer.
*/
if (i > 0)
i--;
block = le16_to_cpu(index[i].ei_leaf_hi);
block = (block << 32) + le32_to_cpu(index[i].ei_leaf_lo);