From: Jan Olszak <j.olszak@samsung.com>
To: Miklos Szeredi <miklos@szeredi.hu>
Cc: David Howells <dhowells@redhat.com>,
"linux-unionfs@vger.kernel.org" <linux-unionfs@vger.kernel.org>
Subject: Re: Optional switching off cow in overlayfs
Date: Mon, 22 Jun 2015 17:32:53 +0200 [thread overview]
Message-ID: <55882AA5.10908@samsung.com> (raw)
In-Reply-To: <CAJfpegtcUt6jR7t_2Ca1osu6+-BKGtnTVVTVXEcWrqBtY0fCzA@mail.gmail.com>
On 06/22/2015 04:37 PM, Miklos Szeredi wrote:
> On Mon, Jun 22, 2015 at 4:26 PM, Jan Olszak <j.olszak@samsung.com> wrote:
>>> You can bind mount individual files from the lower layer to the
>>> overlay. That fixes the "allow modification" part.
>> Well bind mounting every file that should have COW is unmaintainable - if
>> new files appear admin has to mount each one.
> No. I was proposing bind mounts for non-COW ones.
>
> mount -t overlay -olowerdir=/lower,upperdir=/upper,workdir=/work overlay /ovl
> mount --bind /lower/this-file-is-non-cow /ovl/this-file-is-non-cow
> ...
Yes, you are right. This should work, but introduces an overhead of many
mounts for each Linux container.
The proposed alternative is: Use setfattr only once for each file and
then forget about it.
>>> But what should happen on rename or unlink?
>> Both would operate on the original inode.
> And that would make this hugely complex.
Are you sure? I haven't looked into rename and unlink routines but this
patch covers opening the file and is pretty simple (though it probably
breaks fchmod/fchown...).
I can try to prepare a real solution if you like the idea.
From 20e590c0e37f087955b25edfbc2ab4c9c034b5b1 Mon Sep 17 00:00:00 2001
From: Jan Olszak <j.olszak@samsung.com>
Date: Mon, 22 Jun 2015 17:07:31 +0200
Subject: [PATCH] Optional copy on write in overlayfs
---
fs/overlayfs/inode.c | 17 +++++++++++++++++
fs/overlayfs/overlayfs.h | 1 +
fs/overlayfs/super.c | 5 -----
3 files changed, 18 insertions(+), 5 deletions(-)
diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index 04f1248..4f9f399 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -321,6 +321,20 @@ out:
return err;
}
+static bool ovl_dentry_need_copy_up(struct dentry *realdentry)
+{
+ int res;
+ char val;
+ struct inode *inode = realdentry->d_inode;
+
+ res = inode->i_op->getxattr(realdentry, OVL_XATTR_COW, &val, 1);
+ if (res == 1 && val == 'n'){
+ return false;
+ }
+
+ return true;
+}
+
static bool ovl_open_need_copy_up(int flags, enum ovl_path_type type,
struct dentry *realdentry)
{
@@ -330,6 +344,9 @@ static bool ovl_open_need_copy_up(int flags, enum
ovl_path_type type,
if (special_file(realdentry->d_inode->i_mode))
return false;
+ if (!ovl_dentry_need_copy_up(realdentry))
+ return false;
+
if (!(OPEN_FMODE(flags) & FMODE_WRITE) && !(flags & O_TRUNC))
return false;
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index 17ac5af..b364888 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -26,6 +26,7 @@ enum ovl_path_type {
#define OVL_XATTR_PRE_NAME "trusted.overlay."
#define OVL_XATTR_PRE_LEN 16
#define OVL_XATTR_OPAQUE OVL_XATTR_PRE_NAME"opaque"
+#define OVL_XATTR_COW OVL_XATTR_PRE_NAME"cow"
static inline int ovl_do_rmdir(struct inode *dir, struct dentry *dentry)
{
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index bf8537c..916a4b5 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -944,11 +944,6 @@ static int ovl_fill_super(struct super_block *sb,
void *data, int silent)
pr_err("overlayfs: failed to clone lowerpath\n");
goto out_put_lower_mnt;
}
- /*
- * Make lower_mnt R/O. That way fchmod/fchown on lower file
- * will fail instead of modifying lower fs.
- */
- mnt->mnt_flags |= MNT_READONLY;
ufs->lower_mnt[ufs->numlower] = mnt;
ufs->numlower++;
--
1.9.1
Thanks,
Jan
next prev parent reply other threads:[~2015-06-22 15:32 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-18 13:25 Optional switching off cow in overlayfs Jan Olszak
2015-06-18 13:39 ` David Howells
2015-06-18 14:43 ` Jan Olszak
2015-06-22 11:32 ` Miklos Szeredi
2015-06-22 13:45 ` Jan Olszak
2015-06-22 13:53 ` Miklos Szeredi
2015-06-22 14:26 ` Jan Olszak
2015-06-22 14:37 ` Miklos Szeredi
2015-06-22 15:32 ` Jan Olszak [this message]
2015-06-23 9:27 ` David Howells
2015-06-23 10:36 ` Jan Olszak
2015-06-23 13:23 ` David Howells
2015-06-23 16:05 ` Jan Olszak
2015-06-23 16:07 ` Jan Olszak
2015-06-24 16:03 ` Jan Olszak
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