Re: [PATCH 00/18] new API for FS_IOC_[GS]ETFLAGS/FS_IOC_FS[GS]ETXATTR

[Matthew Wilcox]

On Wed, Feb 03, 2021 at 03:13:29PM +0100, Miklos Szeredi wrote:
> On Wed, Feb 3, 2021 at 2:58 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
> 
> > Network filesystems frequently need to use the credentials attached to
> > a struct file in order to communicate with the server.  There's no point
> > fighting this reality.
> 
> IDGI.  Credentials can be taken from the file and from the task.  In
> this case every filesystem except cifs looks at task creds. Why are
> network filesystem special in this respect?

I don't necessarily mean 'struct cred'.  I mean "the authentication
that the client has performed to the server".  Which is not a per-task
thing, it's stored in the struct file, which is why we have things like

        int (*write_begin)(struct file *, struct address_space *mapping,
                                loff_t pos, unsigned len, unsigned flags,
                                struct page **pagep, void **fsdata);

disk filesystems ignore the struct file argument, but network filesystems
very much use it.