On Wed, 10 Oct 2012 13:25:59 -0400
Jeff Layton <jlayton@xxxxxxxxxx> wrote:
> On Wed, 10 Oct 2012 12:22:16 -0500
> Shirish Pargaonkar <shirishpargaonkar@xxxxxxxxx> wrote:
>
> > On Wed, Oct 10, 2012 at 11:14 AM, Jeff Layton <jlayton@xxxxxxxxxx> wrote:
> > > On Wed, 10 Oct 2012 10:11:46 -0500
> > > shirishpargaonkar@xxxxxxxxx wrote:
> > >
> > >> From: Shirish Pargaonkar <shirishpargaonkar@xxxxxxxxx>
> > >>
> > >>
> > >> Add support of Alternate Data Streams (ads).
> > >>
> > >> The generic access flags that cifs client currently employs are sufficient
> > >> for alternate data streams as well (MS-CIFS 2.2.4.64.1).
> > >>
> > >> The stream file and stream type are specified using : after the file name,
> > >> so that is used to differentiate between a regular file and its
> > >> alternate data streams and stream types.
> > >> Since they all have the same file id, each path name,
> > >> file name:stream name:stream type, has a separate inode with that same
> > >> file id but a distinct private data (path name) in that inode to
> > >> distinguish them.
> > >>
> > >> This scheme applies only to non-posix compliant servers such as Windows.
> > >>
> > >> One operation that does not work is Rename (0x7).
> > >>
> > >>
> > >> Signed-off-by: Shirish Pargaonkar <shirishpargaonkar@xxxxxxxxx>
> > >> ---
> > >> fs/cifs/cifsfs.c | 1 +
> > >> fs/cifs/cifsglob.h | 2 ++
> > >> fs/cifs/inode.c | 33 ++++++++++++++++++++++++++++++++-
> > >> 3 files changed, 35 insertions(+), 1 deletions(-)
> > >>
> > >> diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c
> > >> index e7931cc..3068992 100644
> > >> --- a/fs/cifs/cifsfs.c
> > >> +++ b/fs/cifs/cifsfs.c
> > >> @@ -264,6 +264,7 @@ cifs_evict_inode(struct inode *inode)
> > >> {
> > >> truncate_inode_pages(&inode->i_data, 0);
> > >> clear_inode(inode);
> > >> + kfree(inode->i_private);
> > >> cifs_fscache_release_inode_cookie(inode);
> > >> }
> > >>
> > >> diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
> > >> index f5af252..26d65c7 100644
> > >> --- a/fs/cifs/cifsglob.h
> > >> +++ b/fs/cifs/cifsglob.h
> > >> @@ -1251,6 +1251,7 @@ struct dfs_info3_param {
> > >> #define CIFS_FATTR_DELETE_PENDING 0x2
> > >> #define CIFS_FATTR_NEED_REVAL 0x4
> > >> #define CIFS_FATTR_INO_COLLISION 0x8
> > >> +#define CIFS_FATTR_ALTDATASTR 0x10
> > >>
> > >> struct cifs_fattr {
> > >> u32 cf_flags;
> > >> @@ -1268,6 +1269,7 @@ struct cifs_fattr {
> > >> struct timespec cf_atime;
> > >> struct timespec cf_mtime;
> > >> struct timespec cf_ctime;
> > >> + char *cf_private;
> > >> };
> > >>
> > >> static inline void free_dfs_info_param(struct dfs_info3_param *param)
> > >> diff --git a/fs/cifs/inode.c b/fs/cifs/inode.c
> > >> index afdff79..93b010b 100644
> > >> --- a/fs/cifs/inode.c
> > >> +++ b/fs/cifs/inode.c
> > >> @@ -619,6 +619,7 @@ cifs_get_inode_info(struct inode **inode, const char *full_path,
> > >> struct cifs_fattr fattr;
> > >> struct cifs_search_info *srchinf = NULL;
> > >>
> > >> + fattr.cf_private = NULL;
> > >> tlink = cifs_sb_tlink(cifs_sb);
> > >> if (IS_ERR(tlink))
> > >> return PTR_ERR(tlink);
> > >> @@ -746,14 +747,34 @@ cifs_get_inode_info(struct inode **inode, const char *full_path,
> > >> }
> > >>
> > >> if (!*inode) {
> > >> + if (strstr(full_path, ":")) {
I think you probably want strrchr here. You want to
search the string backward. It's possible that the
pathname might have multiple ':' characters in it.
> > >> + fattr.cf_private = kstrdup(full_path, GFP_KERNEL);
Is it really necessary to copy the entire path? This is
a frequently traveled bit of code, and I think you
could save some cycles by just copying the alternate
data stream name.
> > >> + if (!fattr.cf_private) {
> > >> + rc = -ENOMEM;
> > >> + goto cgii_exit;
> > >> + }
> > >> + fattr.cf_flags |= CIFS_FATTR_ALTDATASTR;
> > >> + }
> > >> +
> > >> *inode = cifs_iget(sb, &fattr);
> > >> - if (!*inode)
> > >> + if (*inode) {
> > >> + if (strstr(full_path, ":") &&
> > >> + !((*inode)->i_flags & S_PRIVATE)) {
> > >> + (*inode)->i_private = kstrdup(fattr.cf_private,
> > >> + GFP_KERNEL);
> > >> + if ((*inode)->i_private)
> > >> + (*inode)->i_flags |= S_PRIVATE;
> > >> + else
> > >> + rc = -ENOMEM;
> > >> + }
> > >> + } else
> > >> rc = -ENOMEM;
> > >> } else {
> > >> cifs_fattr_to_inode(*inode, &fattr);
> > >> }
> > >>
> > >> cgii_exit:
> > >> + kfree(fattr.cf_private);
> > >> kfree(buf);
> > >> cifs_put_tlink(tlink);
> > >> return rc;
> > >> @@ -784,6 +805,16 @@ cifs_find_inode(struct inode *inode, void *opaque)
> > >> if (S_ISDIR(inode->i_mode) && !hlist_empty(&inode->i_dentry))
> > >> fattr->cf_flags |= CIFS_FATTR_INO_COLLISION;
> > >>
> > >> + /* looking for an inode of a alternate data stream (full pathname) */
> > >> + if (fattr->cf_flags & CIFS_FATTR_ALTDATASTR) {
> > >> + if (!(inode->i_flags & S_PRIVATE)) {
> > >> + return 0;
> > >> + } else {
> > >> + if (strcmp(inode->i_private, fattr->cf_private))
> > >> + return 0;
> > >> + }
> > >> + }
> > >> +
> > >> return 1;
> > >> }
> > >>
> > >
At least in my cursory testing, it's possible to create an alternate
data stream on a directory as well as a file. The resulting inode does
not seem to be treated as a directory, but what are the implications if
a particular server does?
Also, what's the interaction here with "mapchars" mount option? If
someone specifies that, what behavior should they expect wrt alternate
data streams?
> > > I have real doubts as to whether this patch is necessary. Here's why:
> > >
> > > AIUI, the main concern is that you'll open the "normal" data stream on
> > > the file, cache a bunch of data. Then, if you open the alternate
> > > datastream, the kernel will see that as the same inode -- it'll look
> > > like a hardlink. Then when you go to read, you'll get back the cached
> > > data from the original datastream instead of the alternate one.
> > >
> > > The key point that's missing here is that servers do not hand out
> > > oplocks for alternate data streams. As long as you've mounted in
> > > cache=strict mode (which is the default for 3.7), then there should be
> > > no problem at all, right?
> >
> > Jeff, where does it say that a server should_not/does_not hand out
> > oplocks for an alternate data stream?
> > I have looked for such a documentation and have not found.
> > The one I read,
> > http://msdn.microsoft.com/en-us/library/cc308443.aspx
> > does not mention/preclude alternate data streams from obtaining oplocks.
> >
>
> I believe Jeremy or Chris mentioned it when we were at SDC this year
> and I'm cc'ing them here. I don't recall where they said that was
> stated.
>
...and that does indeed seem to be incorrect. When testing against
win7, if open an alternate data stream on a file (by passing in a ':'
then I do get an oplock.
I have some comments about the above patch though, see above...
--
Jeff Layton <jlayton@xxxxxxxxxx>
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