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

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

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

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
>