[Devel] [PATCH 02/13] ve/fs: Port diff-ve-fs-allow-to-remove-swapfile-hardlinks

[Alexander Mikhalitsyn]

From: Vladimir Davydov <vdavydov at parallels.com>

Author: Maxim Patlasov
Email: MPatlasov at parallels.com
Subject: fs: allow to remove swapfile hardlinks
Date: Tue, 11 Mar 2014 20:33:12 +0400

There is nothing wrong to allow unlink(2) on a swapfile unless this is the last
link (i_nlink == 1).

The patch is useful for sharing a ploop image (which uses the same
S_SWAPFILE flag for protection against truncate as swapfiles) among several
containers by hardlinks. Otherwise, CT destroy would fail due to inability
to unlink image file.

>>>> Nice.
>>>> Why it's not done in upstream?
>>>> I mean, is there any reason against it?
>>>
>>> No, I think. They had solved the problem of lost swapfile by the
>>> simplest patch: disable any unlink.
>>>
>>
>> Are you going to suggest to patch to the upstream?
>> Or it's just our local usage scenario?
>
> It's our own invention -- to use S_SWAPFILE for protection ploop images
> from truncation. Ordinary loop block-device doesn't use it. Nobody else
> (except swapfiles) uses it. So its our local usage from which nobody
> else can get a benefit (until we didn't push ploop upstream in some form).

https://jira.sw.ru/browse/PSBM-25310

Signed-off-by: Maxim Patlasov <MPatlasov at parallels.com>

=============================================================================

Related to https://jira.sw.ru/browse/PSBM-33650

Signed-off-by: Vladimir Davydov <vdavydov at parallels.com>

=============================================================================

VZ 8 rebase part https://jira.sw.ru/browse/PSBM-127782

Signed-off-by: Alexander Mikhalitsyn <alexander.mikhalitsyn at virtuozzo.com>
---
 fs/namei.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/namei.c b/fs/namei.c
index 486e4c587649..52b95f7f1fb6 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2844,7 +2844,8 @@ static int may_delete(struct inode *dir, struct dentry *victim, bool isdir)
 		return -EPERM;
 
 	if (check_sticky(dir, inode) || IS_APPEND(inode) ||
-	    IS_IMMUTABLE(inode) || IS_SWAPFILE(inode) || HAS_UNMAPPED_ID(inode))
+	    IS_IMMUTABLE(inode) || HAS_UNMAPPED_ID(inode) ||
+	    (IS_SWAPFILE(inode) && inode->i_nlink == 1))
 		return -EPERM;
 	if (isdir) {
 		if (!d_is_dir(victim))
-- 
2.28.0