[PATCH 3/3] minix: calculate s_firstdatazone to support more inodes

[Jori Koolstra]

We can potentially ignore the on-disk s_firstdatazone and calculate the
value on the fly instead. Since this field is only a u16, this allows
more inodes to be handled. The mfs implementation in the minix OS does
roughly the same. Currently there is no support for s_firstdatazone=0 in
utils-linux.

Signed-off-by: Jori Koolstra <jkoolstra@xxxxxxxxx>
---
 fs/minix/inode.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/fs/minix/inode.c b/fs/minix/inode.c
index 8eb26ff91adf..d4a43bc86890 100644
--- a/fs/minix/inode.c
+++ b/fs/minix/inode.c
@@ -272,6 +272,15 @@ static int minix_fill_super(struct super_block *s, struct fs_context *fc)
 	} else
 		goto out_no_fs;
 
+	/* We can potentially ignore the on-disk s_firstdatazone and instead
+	 * calculate the value on the fly. Since this field is only a u16,
+	 * this allows more inodes to be handled.
+	 */
+	if (sbi->s_firstdatazone == 0) {
+		sbi->s_firstdatazone = 2 + sbi->s_imap_blocks + sbi->s_zmap_blocks +
+			minix_blocks_needed(sbi->s_ninodes, s->s_blocksize);
+	}
+
 	if (!minix_check_superblock(s))
 		goto out_illegal_sb;
 
-- 
2.51.2