Hi Anssi,
I tested your patch because i faced the same problem. But I need an addition to your patch to get everything to work.
Since for fat12/16 the sect_to_clust() calculation is always a negative value the division through the cluster size with an odd negative value cuts the rest. With the next clust_to_sect() call the now even cluster number is multiplied by the cluster size and and the data_begin section is added. So after the calculation without the rest the negative value is smaller and my rootdir_sect is higher then the actual rootdir_sect. In my case: clust_size = 2 rootdir_sect = 113 dara_begin = 132
sect_to_clust: 0xfffffff1 = (0x113 - 132) / 2 sect_to_clust: 114 = 132 + 0xfffffff1 * 2
Now my root_cluster is above the root dir but it should be below it (112). I fixed this with the following patch:
---
fs/fat/fat.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/fs/fat/fat.c b/fs/fat/fat.c index de5c7210be..695b6323b1 100644 --- a/fs/fat/fat.c +++ b/fs/fat/fat.c @@ -587,7 +587,9 @@ static int get_fs_info(fsdata *mydata) mydata->rootdir_size - (mydata->clust_size * 2); mydata->root_cluster = - sect_to_clust(mydata, mydata->rootdir_sect); + sect_to_clust(mydata, mydata->rootdir_sect - + (mydata->rootdir_sect % + mydata->clust_size)); }
mydata->fatbufnum = -1;
After patch: sect_to_clust: 0xfffffff0 = (0x112 - 132) / 2 sect_to_clust: 112 = 132 + 0xfffffff0 * 2
Can you verify this? If yes? Is it maybe possible to add this to your patch?
Regards, Bernhard