On Sat, Dec 23, 2023 at 8:54 AM Amir Goldstein <amir73il@xxxxxxxxx> wrote:
>
> On Fri, Dec 22, 2023 at 2:54 PM Christian Brauner <brauner@xxxxxxxxxx> wrote:
> >
> > On Thu, Dec 21, 2023 at 11:54:10AM +0200, Amir Goldstein wrote:
> > > Assert that the file object is allocated in a backing_file container
> > > so that file_user_path() could be used to display the user path and
> > > not the backing file's path in /proc/<pid>/maps.
> > >
> > > Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
> > > ---
> > > fs/backing-file.c | 27 +++++++++++++++++++++++++++
> > > fs/overlayfs/file.c | 23 ++++++-----------------
> > > include/linux/backing-file.h | 2 ++
> > > 3 files changed, 35 insertions(+), 17 deletions(-)
> > >
> > > diff --git a/fs/backing-file.c b/fs/backing-file.c
> > > index 46488de821a2..1ad8c252ec8d 100644
> > > --- a/fs/backing-file.c
> > > +++ b/fs/backing-file.c
> > > @@ -11,6 +11,7 @@
> > > #include <linux/fs.h>
> > > #include <linux/backing-file.h>
> > > #include <linux/splice.h>
> > > +#include <linux/mm.h>
> > >
> > > #include "internal.h"
> > >
> > > @@ -284,6 +285,32 @@ ssize_t backing_file_splice_write(struct pipe_inode_info *pipe,
> > > }
> > > EXPORT_SYMBOL_GPL(backing_file_splice_write);
> > >
> > > +int backing_file_mmap(struct file *file, struct vm_area_struct *vma,
> > > + struct backing_file_ctx *ctx)
> > > +{
> > > + const struct cred *old_cred;
> > > + int ret;
> > > +
> > > + if (WARN_ON_ONCE(!(file->f_mode & FMODE_BACKING)) ||
> >
> > Couldn't that WARN_ON_ONCE() be in every one of these helpers in this
> > series? IOW, when would you ever want to use a backing_file_*() helper
> > on a non-backing file?
>
> AFAIK, the call chain below backing_file_splice*() and backing_file_*_iter()
> helpers never end up accessing file_user_path() or assuming that fd of file
> is installed in fd table, so there is no strong reason to enforce this with an
> assertion.
>
> We can do it for clarity of semantics, in case one of the call chains will
> start assuming a struct backing_file in the future. WDIT?
Doh! WDYT?
Thanks,
Amir.
