[source] kernel: Fix the incorrect i_nlink count after jffs2's RENAME_EXCHANGE operations.

[LEDE Commits]

nbd pushed a commit to source.git, branch lede-17.01:
https://git.lede-project.org/638ca50f3b1d66fb165891552ed8cde31aa2f194

commit 638ca50f3b1d66fb165891552ed8cde31aa2f194
Author: Jing Qiu <aqiu0720 at gmail.com>
AuthorDate: Tue Mar 14 15:32:08 2017 +0800

    kernel: Fix the incorrect i_nlink count after jffs2's RENAME_EXCHANGE operations.
    
    The problem is caused by the incorrect handling of the parent inode's
    i_nlink count for the dentry to be RENAME_EXCHANGED. There are 3 cases
    to consider. Assume we want to RENAME_EXCHANGE struct dentry *a and
    struct dentry *b, and inode_a is pointed to by dentry_a, inode_b is
    pointed to by dentry_b:
    
    1. If inode_a is a directory, but inode_b isn't, then we must decrease
       the i_nlink count of old_dir_i, and increase the i_nlink of new_dir_i.
    2. If inode_a isn't a directory, but inode_b is a directory, then we
       must increase the i_nlink of old_dir_i, and decrease the i_nlink count
       of new_dir_i.
    3. If the types of inode_a and inode_b are the same, we don't change the
       i_nlink for either old_dir_i or new_dir_i.
    
    Signed-off-by: Jing Qiu <aqiu0720 at gmail.com>
    Signed-off-by: Felix Fietkau <nbd at nbd.name>
---
 .../111-jffs2-add-RENAME_EXCHANGE-support.patch    | 33 ++++++++++++++++++----
 1 file changed, 28 insertions(+), 5 deletions(-)

diff --git a/target/linux/generic/patches-4.4/111-jffs2-add-RENAME_EXCHANGE-support.patch b/target/linux/generic/patches-4.4/111-jffs2-add-RENAME_EXCHANGE-support.patch
index b624087..37eb073 100644
--- a/target/linux/generic/patches-4.4/111-jffs2-add-RENAME_EXCHANGE-support.patch
+++ b/target/linux/generic/patches-4.4/111-jffs2-add-RENAME_EXCHANGE-support.patch
@@ -7,7 +7,12 @@ Signed-off-by: Felix Fietkau <nbd at nbd.name>
 
 --- a/fs/jffs2/dir.c
 +++ b/fs/jffs2/dir.c
-@@ -782,7 +782,7 @@ static int jffs2_rename (struct inode *o
+@@ -779,18 +779,31 @@ static int jffs2_rename (struct inode *o
+ 	int ret;
+ 	struct jffs2_sb_info *c = JFFS2_SB_INFO(old_dir_i->i_sb);
+ 	struct jffs2_inode_info *victim_f = NULL;
++	struct inode *fst_inode = d_inode(old_dentry);
++	struct inode *snd_inode = d_inode(new_dentry);
  	uint8_t type;
  	uint32_t now;
  
@@ -15,8 +20,19 @@ Signed-off-by: Felix Fietkau <nbd at nbd.name>
 +	if (flags & ~(RENAME_WHITEOUT | RENAME_EXCHANGE))
  		return -EINVAL;
  
++	if ((flags & RENAME_EXCHANGE) && (old_dir_i != new_dir_i)) {
++		if (S_ISDIR(fst_inode->i_mode) && !S_ISDIR(snd_inode->i_mode)) {
++			inc_nlink(new_dir_i);
++			drop_nlink(old_dir_i);
++		}
++		else if (!S_ISDIR(fst_inode->i_mode) && S_ISDIR(snd_inode->i_mode)) {
++			drop_nlink(new_dir_i);
++			inc_nlink(old_dir_i);
++		}
++	}
++
  	/* The VFS will check for us and prevent trying to rename a
-@@ -790,7 +790,7 @@ static int jffs2_rename (struct inode *o
+ 	 * file over a directory and vice versa, but if it's a directory,
  	 * the VFS can't check whether the victim is empty. The filesystem
  	 * needs to do that for itself.
  	 */
@@ -25,7 +41,7 @@ Signed-off-by: Felix Fietkau <nbd at nbd.name>
  		victim_f = JFFS2_INODE_INFO(d_inode(new_dentry));
  		if (d_is_dir(new_dentry)) {
  			struct jffs2_full_dirent *fd;
-@@ -825,7 +825,7 @@ static int jffs2_rename (struct inode *o
+@@ -825,7 +838,7 @@ static int jffs2_rename (struct inode *o
  	if (ret)
  		return ret;
  
@@ -34,7 +50,14 @@ Signed-off-by: Felix Fietkau <nbd at nbd.name>
  		/* There was a victim. Kill it off nicely */
  		if (d_is_dir(new_dentry))
  			clear_nlink(d_inode(new_dentry));
-@@ -851,6 +851,12 @@ static int jffs2_rename (struct inode *o
+@@ -845,12 +858,18 @@ static int jffs2_rename (struct inode *o
+ 
+ 	/* If it was a directory we moved, and there was no victim,
+ 	   increase i_nlink on its new parent */
+-	if (d_is_dir(old_dentry) && !victim_f)
++	if (d_is_dir(old_dentry) && !victim_f && !(flags & RENAME_EXCHANGE))
+ 		inc_nlink(new_dir_i);
+ 
  	if (flags & RENAME_WHITEOUT)
  		/* Replace with whiteout */
  		ret = jffs2_whiteout(old_dir_i, old_dentry);
@@ -47,7 +70,7 @@ Signed-off-by: Felix Fietkau <nbd at nbd.name>
  	else
  		/* Unlink the original */
  		ret = jffs2_do_unlink(c, JFFS2_INODE_INFO(old_dir_i),
-@@ -882,7 +888,7 @@ static int jffs2_rename (struct inode *o
+@@ -882,7 +901,7 @@ static int jffs2_rename (struct inode *o
  		return ret;
  	}