[PATCH 1/3] fs/ntfs3: Add comments about cluster size

Konstantin Komarov
2022-09-12T16:39:22Z

This commit adds additional info about CONFIG_NTFS3_64BIT_CLUSTER

Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>
---
fs/ntfs3/frecord.c | 2 +-
fs/ntfs3/record.c | 4 ++++
fs/ntfs3/super.c | 24 +++++++++++++++++++++++++++
3 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/fs/ntfs3/frecord.c b/fs/ntfs3/frecord.c
index 381a38a06ec2..b752d83cf460 100644
--- a/fs/ntfs3/frecord.c
+++ b/fs/ntfs3/frecord.c
@@ -557,7 +557,7 @@ static int ni_repack(struct ntfs_inode *ni)
}

if (!mi_p) {
- /* Do not try if not enogh free space. */
+ /* Do not try if not enough free space. */
if (le32_to_cpu(mi->mrec->used) + 8 >= rs)
continue;

diff --git a/fs/ntfs3/record.c b/fs/ntfs3/record.c
index 7d2fac5ee215..c8741cfa421f 100644
--- a/fs/ntfs3/record.c
+++ b/fs/ntfs3/record.c
@@ -537,6 +537,10 @@ bool mi_resize_attr(struct mft_inode *mi, struct ATTRIB *attr, int bytes)
return true;
}

+/*
+ * Pack runs in MFT record.
+ * If failed record is not changed.
+ */
int mi_pack_runs(struct mft_inode *mi, struct ATTRIB *attr,
struct runs_tree *run, CLST len)
{
diff --git a/fs/ntfs3/super.c b/fs/ntfs3/super.c
index 47012c9bf505..86ff55133faf 100644
--- a/fs/ntfs3/super.c
+++ b/fs/ntfs3/super.c
@@ -21,6 +21,30 @@
* https://docs.microsoft.com/en-us/windows/wsl/file-permissions
* It stores uid/gid/mode/dev in xattr
*
+ * ntfs allows up to 2^64 clusters per volume.
+ * It means you should use 64 bits lcn to operate with ntfs.
+ * Implementation of ntfs.sys uses only 32 bits lcn.
+ * Default ntfs3 uses 32 bits lcn too.
+ * ntfs3 built with CONFIG_NTFS3_64BIT_CLUSTER (ntfs3_64) uses 64 bits per lcn.
+ *
+ *
+ * ntfs limits, cluster size is 4K (2^12)
+ * -----------------------------------------------------------------------------
+ * | Volume size | Clusters | ntfs.sys | ntfs3 | ntfs3_64 | mkntfs | chkdsk |
+ * -----------------------------------------------------------------------------
+ * | < 16T, 2^44 | < 2^32 | yes | yes | yes | yes | yes |
+ * | > 16T, 2^44 | > 2^32 | no | no | yes | yes | yes |
+ * ----------------------------------------------------------|------------------
+ *
+ * To mount large volumes as ntfs one should use large cluster size (up to 2M)
+ * The maximum volume size in this case is 2^32 * 2^21 = 2^53 = 8P
+ *
+ * ntfs limits, cluster size is 2M (2^31)
+ * -----------------------------------------------------------------------------
+ * | < 8P, 2^54 | < 2^32 | yes | yes | yes | yes | yes |
+ * | > 8P, 2^54 | > 2^32 | no | no | yes | yes | yes |
+ * ----------------------------------------------------------|------------------
+ *
*/

#include <linux/blkdev.h>
--
2.37.0