On 02/12/2014 01:25 AM, Alex Elder wrote:
> On 02/11/2014 09:10 AM, Yan, Zheng wrote:
>> On Tue, Feb 11, 2014 at 10:47 PM, Alex Elder <elder@xxxxxxxx> wrote:
>>> On 02/10/2014 11:30 PM, Yan, Zheng wrote:
>>>> Signed-off-by: Yan, Zheng <zheng.z.yan@xxxxxxxxx>
>>>
>>> You really need to explain better under what circumstances
>>> a zero-size xattr is getting removed.
>>>
>>> But apparently it's only when you're updating an xattr
>>> (not building it up from a blob from storage).
>>>
>>> Why are you doing this? Why can't an xattr exist with
>>> an empty value?
>>
>> That is how other FS behave, at least for ext* and btrfs.
>
> I haven't tested this, I'm just glancing through code.
> But it looks to me like a zero-length value is OK, but
> a null value pointer means it should be deleted. Note
> in btrfs_setxattr(), for example, the same bit of code
> I referenced before:
>
> if (size == 0)
> value = ""; /* empty EA, do not remove */
>
> And ext4 seems to delete for a null value, but handle
> an xattr whose value *length* is zero. Same with XFS.
>
> So again, I haven't verified through testing, but my
> reading of the code (though rusty) still seems to show
> that an attribute can have an empty (zero-size) value.
You are right, Thanks. how about below patch?
---
>From f11d5da84230e4993333a063019bad68c67b50d4 Mon Sep 17 00:00:00 2001
From: "Yan, Zheng" <zheng.z.yan@xxxxxxxxx>
Date: Tue, 11 Feb 2014 13:04:19 +0800
Subject: [PATCH 2/5] ceph: remove xattr when null value is given to setxattr()
For the setxattr request, introduce a new flag CEPH_XATTR_REMOVE
to distinguish null value case from the zero-length value case.
Signed-off-by: Yan, Zheng <zheng.z.yan@xxxxxxxxx>
---
fs/ceph/xattr.c | 16 ++++++++++++++--
include/linux/ceph/ceph_fs.h | 5 +++--
2 files changed, 17 insertions(+), 4 deletions(-)
diff --git a/fs/ceph/xattr.c b/fs/ceph/xattr.c
index 28f9793..f6becf6 100644
--- a/fs/ceph/xattr.c
+++ b/fs/ceph/xattr.c
@@ -12,6 +12,9 @@
#define XATTR_CEPH_PREFIX "ceph."
#define XATTR_CEPH_PREFIX_LEN (sizeof (XATTR_CEPH_PREFIX) - 1)
+static int __remove_xattr(struct ceph_inode_info *ci,
+ struct ceph_inode_xattr *xattr);
+
/*
* List of handlers for synthetic system.* attributes. Other
* attributes are handled directly.
@@ -359,6 +362,12 @@ static int __set_xattr(struct ceph_inode_info *ci,
kfree(val);
return err;
}
+ if (update_xattr < 0) {
+ if (xattr)
+ __remove_xattr(ci, xattr);
+ kfree(name);
+ return 0;
+ }
}
if (!xattr) {
@@ -862,6 +871,9 @@ static int ceph_sync_setxattr(struct dentry *dentry, const char *name,
dout("setxattr value=%.*s\n", (int)size, value);
+ if (!value)
+ flags |= CEPH_XATTR_REMOVE;
+
/* do request */
req = ceph_mdsc_create_request(mdsc, CEPH_MDS_OP_SETXATTR,
USE_AUTH_MDS);
@@ -965,8 +977,8 @@ retry:
goto retry;
}
- err = __set_xattr(ci, newname, name_len, newval,
- val_len, flags, 1, &xattr);
+ err = __set_xattr(ci, newname, name_len, newval, val_len,
+ flags, val ? 1 : -1, &xattr);
if (!err) {
dirty = __ceph_mark_dirty_caps(ci, CEPH_CAP_XATTR_EXCL);
diff --git a/include/linux/ceph/ceph_fs.h b/include/linux/ceph/ceph_fs.h
index 2623cff..25bfb0e 100644
--- a/include/linux/ceph/ceph_fs.h
+++ b/include/linux/ceph/ceph_fs.h
@@ -373,8 +373,9 @@ extern const char *ceph_mds_op_name(int op);
/*
* Ceph setxattr request flags.
*/
-#define CEPH_XATTR_CREATE 1
-#define CEPH_XATTR_REPLACE 2
+#define CEPH_XATTR_CREATE (1 << 0)
+#define CEPH_XATTR_REPLACE (1 << 1)
+#define CEPH_XATTR_REMOVE (1 << 31)
union ceph_mds_request_args {
struct {
--
1.8.5.3
>
> -Alex
>
>> Regards
>> Yan, Zheng
>>
>>>
>>> Looking at generic_setxattr() in "fs/xattr.c" we see:
>>> if (size == 0)
>>> value = ""; /* empty EA, do not remove */
>>>
>>> The code you have below looks OK, but it seems that you
>>> shouldn't be doing this.
>>>
>>> Am I missing something?
>>>
>>> -Alex
>>>
>>>> ---
>>>> fs/ceph/xattr.c | 9 +++++++++
>>>> 1 file changed, 9 insertions(+)
>>>>
>>>> diff --git a/fs/ceph/xattr.c b/fs/ceph/xattr.c
>>>> index 28f9793..6ed0e5a 100644
>>>> --- a/fs/ceph/xattr.c
>>>> +++ b/fs/ceph/xattr.c
>>>> @@ -12,6 +12,9 @@
>>>> #define XATTR_CEPH_PREFIX "ceph."
>>>> #define XATTR_CEPH_PREFIX_LEN (sizeof (XATTR_CEPH_PREFIX) - 1)
>>>>
>>>> +static int __remove_xattr(struct ceph_inode_info *ci,
>>>> + struct ceph_inode_xattr *xattr);
>>>> +
>>>> /*
>>>> * List of handlers for synthetic system.* attributes. Other
>>>> * attributes are handled directly.
>>>> @@ -359,6 +362,12 @@ static int __set_xattr(struct ceph_inode_info *ci,
>>>> kfree(val);
>>>> return err;
>>>> }
>>>> + if (!val_len) {
>>>> + if (xattr)
>>>> + __remove_xattr(ci, xattr);
>>>> + kfree(name);
>>>> + return 0;
>>>> + }
>>>> }
>>>>
>>>> if (!xattr) {
>>>>
>>>
>>> --
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