max file size for ext3

["Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx>]

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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