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Hello again

In my ext2 implementation, I assume block group descriptor table is 1 block. Is that always correct? I'm not sure it is correct, because with the size of block group descriptor is 32 bytes, and with 1024 bytes of block size, a block can have only 32 block group descriptors. (1024 / 32 = 32) With 1024 bytes of block size, a block group descriptor can only handle 8 megabytes. With 32 block group descriptors, entire ext2 can handle only 256 megabytes. (8 * 32 = 256)

But I'm still not sure
In wiki.osdev.org/Ext2 it says we can find block group count with "Rounding up the total number of blocks divided by the number of blocks per block group".

If I round block group count to (block size in bytes / 32), can I found size of block group descriptor table in blocks?

If not, how can I?

Thanks

If you read the documentation ( http://www.nongnu.org/ext2-doc/ext2.html ) it explains that the table can be one or more blocks in size. That document should answer all your questions.

You need to calculate how many blocks the block group descriptors occupy

iansjack wrote:If you read the documentation ( http://www.nongnu.org/ext2-doc/ext2.html ) it explains that the table can be one or more blocks in size. That document should answer all your questions.

Oh, that was my bad. I didn't read it, but I only read the disk organization and assumed it is only one block. ("1 block - block group descriptor table" from Chapter 3, Table 3-2. Sample 20mb Partition Layout)

Thanks

crunch wrote:You need to calculate how many blocks the block group descriptors occupy

Code: Select all

num_to_read = ((num_block_groups * sizeof(struct ext2_group_desc)) / blocksize) + 1;

Thanks, that works, but it reads a block more.

With 32 block groups, and 32 bytes (size of group descriptor) (1024 / 1024) + 1 equals 2
I think the correct one is That is (1023 / 1024) + 1 and results one.

Thanks

I was just trying to see if you were paying attention