Re: [PATCH v3 02/10] xattr: add a function to check if a namespace is supported

[Frank van der Linden <fllinden@amazon.com>]

On Thu, Jun 25, 2020 at 08:41:57PM +0000, Frank van der Linden wrote:
> Hi Al,
> 
> ..and here is the other xattr change that was part of the nfsd user xattr
> support series that I mentioned in my previous email.
> 
> Full series here:
> 
> https://lore.kernel.org/linux-nfs/20200623223927.31795-1-fllinden@amazon.com/
> 
> Any comments / concerned about this one?
> 
> Thanks,
> 
> - Frank

Hi Al,

Here's the other one I'm just sending a quick ping on. It's a simple change -
just add a little new function that enables nfsd to check if the "user."
namespace is at all supported by a filesystem.

Any comments?

Again, Linus - this is a pretty small change, doesn't affect any existing
codepaths, and it's already in the tree Chuck is setting up for 5.9. Could
this go in through that directly?

Thanks,

- Frank
> 
> On Tue, Jun 23, 2020 at 10:39:19PM +0000, Frank van der Linden wrote:
> > Add a function that checks is an extended attribute namespace is
> > supported for an inode, meaning that a handler must be present
> > for either the whole namespace, or at least one synthetic
> > xattr in the namespace.
> > 
> > To be used by the nfs server code when being queried for extended
> > attributes support.
> > 
> > Cc: linux-fsdevel@vger.kernel.org
> > Cc: Al Viro <viro@zeniv.linux.org.uk>
> > Signed-off-by: Frank van der Linden <fllinden@amazon.com>
> > ---
> >  fs/xattr.c            | 27 +++++++++++++++++++++++++++
> >  include/linux/xattr.h |  2 ++
> >  2 files changed, 29 insertions(+)
> > 
> > diff --git a/fs/xattr.c b/fs/xattr.c
> > index 95f38f57347f..386b45676d7e 100644
> > --- a/fs/xattr.c
> > +++ b/fs/xattr.c
> > @@ -134,6 +134,33 @@ xattr_permission(struct inode *inode, const char *name, int mask)
> >  	return inode_permission(inode, mask);
> >  }
> >  
> > +/*
> > + * Look for any handler that deals with the specified namespace.
> > + */
> > +int
> > +xattr_supported_namespace(struct inode *inode, const char *prefix)
> > +{
> > +	const struct xattr_handler **handlers = inode->i_sb->s_xattr;
> > +	const struct xattr_handler *handler;
> > +	size_t preflen;
> > +
> > +	if (!(inode->i_opflags & IOP_XATTR)) {
> > +		if (unlikely(is_bad_inode(inode)))
> > +			return -EIO;
> > +		return -EOPNOTSUPP;
> > +	}
> > +
> > +	preflen = strlen(prefix);
> > +
> > +	for_each_xattr_handler(handlers, handler) {
> > +		if (!strncmp(xattr_prefix(handler), prefix, preflen))
> > +			return 0;
> > +	}
> > +
> > +	return -EOPNOTSUPP;
> > +}
> > +EXPORT_SYMBOL(xattr_supported_namespace);
> > +
> >  int
> >  __vfs_setxattr(struct dentry *dentry, struct inode *inode, const char *name,
> >  	       const void *value, size_t size, int flags)
> > diff --git a/include/linux/xattr.h b/include/linux/xattr.h
> > index a2f3cd02653c..fac75810d9d3 100644
> > --- a/include/linux/xattr.h
> > +++ b/include/linux/xattr.h
> > @@ -61,6 +61,8 @@ ssize_t generic_listxattr(struct dentry *dentry, char *buffer, size_t buffer_siz
> >  ssize_t vfs_getxattr_alloc(struct dentry *dentry, const char *name,
> >  			   char **xattr_value, size_t size, gfp_t flags);
> >  
> > +int xattr_supported_namespace(struct inode *inode, const char *prefix);
> > +
> >  static inline const char *xattr_prefix(const struct xattr_handler *handler)
> >  {
> >  	return handler->prefix ?: handler->name;
> > -- 
> > 2.17.2
> >