On Wed, 12 Feb 2014, Yan, Zheng wrote:
> 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,
How about just turning this into a REMOVEXATTR request in the !value case?
sage
> 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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