Re: [PATCH -V4 6/6] x86: Add new syscalls for x86_64

["Aneesh Kumar K. V" <aneesh.kumar@linux.vnet.ibm.com>]

On Fri, 23 Apr 2010 16:09:07 -0600, Andreas Dilger <adilger@sun.com> wrote:
> On 2010-04-23, at 05:38, Aneesh Kumar K.V wrote:
> > Add necessary compat syscall support
> 
> Maybe I'm missing something, but why would we add a new syscall that immediately needs a compat interface?  I thought the kernel would simply return the packed file handle to userspace, instead of returning a pointer?
> 
> > +struct compat_file_handle {
> > +	int handle_size;
> > +	int handle_type;
> > +	/* File system identifier */
> > +	struct uuid fsid;
> > +	/* file identifier */
> > +	compat_uptr_t f_handle;
> > +};
> 


I want to make sure we put uuid part of the fs as a separate member. I
guess we could avoid compat interface if we define the syscall as

open_by_handle(struct file_handle *handle, int size, int flags);

But the handle in the above case will not be usable if the file handle
returned is too big to be usable by a cluster file system because of the
UUID part of handle. Having uuid as a seperate member allows such userspace
to generate a smaller unique identifier for the filesystem and still use
the void *f_handle part of the struct file_handle.

With struct file_handle since we have void * usage i guess we would need
a compat interface.

-aneesh