Hi,
I am looking at ext4_max_size and was confused how the
number upper_limit = 0x1ff7fffd000LL is arrived.
The comment says the value is arrived looking at 4K.
So i tried the below program.
main()
{
unsigned long long upper_limit, meta_blocks;
int bits = 12;
/* total blocks in 512 bytes */
upper_limit = (1LL << 32) - 1;
/* total blocks in file system block size */
upper_limit >>= (bits - 9);
meta_blocks = 1;
/* double indirect blocks */
meta_blocks += 1 + 1LL << (bits-2);
/* tripple indirect blocks */
meta_blocks += 1 + 1LL << (bits-2) + 1LL << (2*(bits-2));
upper_limit -= meta_blocks;
upper_limit <<= bits;
printf("%x\n", upper_limit);
}
Can somebody help me to find out what is missing in the above ?
I also think hardcoding 4k block size is not correct. I have the below
patch pending with large file size.
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 2083c19..9f39cfb 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1511,6 +1511,7 @@ static void ext4_orphan_cleanup (struct super_block * sb,
static loff_t ext4_max_size(int bits, struct super_block *sb)
{
loff_t res = EXT4_NDIR_BLOCKS;
+ loff_t total_meta_blocks;
/* This constant is calculated to be the largest file size for a
* dense, 4k-blocksize file such that the total number of
* sectors in the file, including data and all indirect blocks,
@@ -1518,11 +1519,34 @@ static loff_t ext4_max_size(int bits, struct
super_block *sb)
loff_t upper_limit;
if (EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_LARGE_BLOCK)) {
- /* FIXME!! */
- upper_limit = (1LL << (bits + 32)) - 1;
+ /*
+ * With __u32 i_blocks representing the total number of blocks
+ * of the file in file system block size, the max file size
+ * would be 2**(32) - 1 - blocks taken by the meta data
+ * blocks multiplied by block size.
+ */
+ /* total blocks in file system block size*/
+ upper_limit = (1LL << 32) - 1;
+
} else {
- upper_limit = 0x1ff7fffd000LL;
+ /* total blocks in 512 bytes */
+ upper_limit = (1LL << 32) - 1;
+ /* total blocks in file system block size */
+ upper_limit >>= (bits - 9);
+
+ //upper_limit = 0x1ff7fffd000LL;
}
+
+ /* indirect blocks */
+ meta_blocks = 1;
+ /* double indirect blocks */
+ meta_blocks += 1 + 1LL << (bits-2);
+ /* tripple indirect blocks */
+ meta_blocks += 1 + 1LL << (bits-2) + 1LL << (2*(bits-2));
+
+ upper_limit -= meta_blocks;
+ upper_limit <<= bits;
+
res += 1LL << (bits-2);
res += 1LL << (2*(bits-2));
res += 1LL << (3*(bits-2));
-
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