On Aug 30, 2011, at 3:18 PM, Jeff Layton wrote:
> On Mon, 29 Aug 2011 14:51:15 -0400
> Chuck Lever <chuck.lever@xxxxxxxxxx> wrote:
>
>> From: Trond Myklebust <Trond.Myklebust@xxxxxxxxxx>
>>
>> Signed-off-by: Trond Myklebust <Trond.Myklebust@xxxxxxxxxx>
>> [ cel: since this is server-side, use nfsd4_ prefix instead of nfs4_ prefix. ]
>> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
>> ---
>>
>> fs/nfsd/nfsd.h | 7 +++++++
>> fs/nfsd/vfs.c | 15 +++++++++++++++
>> 2 files changed, 22 insertions(+), 0 deletions(-)
>>
>> diff --git a/fs/nfsd/nfsd.h b/fs/nfsd/nfsd.h
>> index 7ecfa24..d314812 100644
>> --- a/fs/nfsd/nfsd.h
>> +++ b/fs/nfsd/nfsd.h
>> @@ -335,6 +335,13 @@ static inline u32 nfsd_suppattrs2(u32 minorversion)
>> #define NFSD_SUPPATTR_EXCLCREAT_WORD2 \
>> NFSD_WRITEABLE_ATTRS_WORD2
>>
>> +extern int nfsd4_is_junction(struct dentry *dentry);
>> +#else
>> +static inline int nfsd4_is_junction(struct dentry *dentry)
>> +{
>> + return 0;
>> +}
>> +
>> #endif /* CONFIG_NFSD_V4 */
>>
>> #endif /* LINUX_NFSD_NFSD_H */
>> diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
>> index fd0acca..5dac667 100644
>> --- a/fs/nfsd/vfs.c
>> +++ b/fs/nfsd/vfs.c
>> @@ -168,6 +168,8 @@ int nfsd_mountpoint(struct dentry *dentry, struct svc_export *exp)
>> {
>> if (d_mountpoint(dentry))
>> return 1;
>> + if (nfsd4_is_junction(dentry))
>> + return 1;
>> if (!(exp->ex_flags & NFSEXP_V4ROOT))
>> return 0;
>> return dentry->d_inode != NULL;
>> @@ -592,6 +594,19 @@ nfsd4_get_nfs4_acl(struct svc_rqst *rqstp, struct dentry *dentry, struct nfs4_ac
>> return error;
>> }
>>
>> +#define NFSD_XATTR_JUNCTION_PREFIX XATTR_TRUSTED_PREFIX "junction."
>> +#define NFSD_XATTR_JUNCTION_TYPE NFSD_XATTR_JUNCTION_PREFIX "type"
>> +int nfsd4_is_junction(struct dentry *dentry)
>> +{
>> + ssize_t ret;
>> +
>> + if (dentry->d_inode != NULL) {
>> + ret = vfs_getxattr(dentry, NFSD_XATTR_JUNCTION_TYPE, NULL, 0);
>> + if (ret > 0)
>> + return 1;
>> + }
>> + return 0;
>> +}
>
> Won't the above check be rather expensive? You'll need to do a
> getxattr call on almost every path component of every lookup, right?
>
> I may be misremembering your talk from connectathon, but I thought you
> were planning to use a well-known mode for junctions that would cut
> down on the number of unnecessary getxattrs...
Yes, that's the plan. To reduce overhead, the S_ISVTX bit must be set before NFSD does the expensive xattr test. However, I don't think this kind of filtering was ever implemented. I got the patch from here:
http://git.linux-nfs.org/?p=trondmy/nfs-2.6.git;a=shortlog;h=refs/heads/fedfs-for-2.6.34
and that doesn't seem to have it either. I can implement something and repost these.
>> #endif /* defined(CONFIG_NFSD_V4) */
>>
>> #ifdef CONFIG_NFSD_V3
>>
>> --
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>
>
> --
> Jeff Layton <jlayton@xxxxxxxxxxxxxxx>
--
Chuck Lever
chuck[dot]lever[at]oracle[dot]com
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