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

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Message-ID: <c1fd8894-aaba-c5ff-57f2-480c480880f7@paragon-software.com>
Date:   Mon, 12 Sep 2022 19:39:19 +0300
From:   Konstantin Komarov <almaz.alexandrovich@...agon-software.com>
To:     <ntfs3@...ts.linux.dev>
CC:     <linux-kernel@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>
Subject: [PATCH 1/3] fs/ntfs3: Add comments about cluster size

This commit adds additional info about CONFIG_NTFS3_64BIT_CLUSTER

Signed-off-by: Konstantin Komarov <almaz.alexandrovich@...agon-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