[Intel-gfx] [PATCH v14 20/26] iommufd: Add iommufd_ctx_from_fd()

[Liu, Yi L]

> From: Jason Gunthorpe <jgg at nvidia.com>
> Sent: Friday, July 14, 2023 10:21 PM
> 
> On Mon, Jul 10, 2023 at 07:59:22PM -0700, Yi Liu wrote:
> > It's common to get a reference to the iommufd context from a given file
> > descriptor. So adds an API for it. Existing users of this API are compiled
> > only when IOMMUFD is enabled, so no need to have a stub for the IOMMUFD
> > disabled case.
> >
> > Signed-off-by: Yi Liu <yi.l.liu at intel.com>
> > ---
> >  drivers/iommu/iommufd/main.c | 23 +++++++++++++++++++++++
> >  include/linux/iommufd.h      |  1 +
> >  2 files changed, 24 insertions(+)
> >
> > diff --git a/drivers/iommu/iommufd/main.c b/drivers/iommu/iommufd/main.c
> > index 32ce7befc8dd..e99a338d4fdf 100644
> > --- a/drivers/iommu/iommufd/main.c
> > +++ b/drivers/iommu/iommufd/main.c
> > @@ -377,6 +377,29 @@ struct iommufd_ctx *iommufd_ctx_from_file(struct file *file)
> >  }
> >  EXPORT_SYMBOL_NS_GPL(iommufd_ctx_from_file, IOMMUFD);
> >
> > +/**
> > + * iommufd_ctx_from_fd - Acquires a reference to the iommufd context
> > + * @fd: File descriptor to obtain the reference from
> > + *
> > + * Returns a pointer to the iommufd_ctx, otherwise ERR_PTR. On success
> > + * the caller is responsible to call iommufd_ctx_put().
> > + */
> > +struct iommufd_ctx *iommufd_ctx_from_fd(int fd)
> > +{
> > +	struct iommufd_ctx *iommufd;
> > +	struct fd f;
> > +
> > +	f = fdget(fd);
> > +	if (!f.file)
> > +		return ERR_PTR(-EBADF);
> > +
> > +	iommufd = iommufd_ctx_from_file(f.file);
> > +
> > +	fdput(f);
> > +	return iommufd;
> > +}
> > +EXPORT_SYMBOL_NS_GPL(iommufd_ctx_from_fd, IOMMUFD);
> 
> This is a little wonky since iommufd_ctx_from_file() also obtains a
> reference

Yes. that's why need fdput() always.

> Just needs to be like this:
> 
> struct iommufd_ctx *iommufd_ctx_from_fd(int fd)
> {
> 	struct file *file;
> 
> 	file = fget(fd);
> 	if (!file)
> 		return ERR_PTR(-EBADF);
> 
> 	if (file->f_op != &iommufd_fops) {
> 		fput(file);
> 		return ERR_PTR(-EBADFD);
> 	}
> 	/* fget is the same as iommufd_ctx_get() */
> 	return file->private_data;
> }
> EXPORT_SYMBOL_NS_GPL(iommufd_ctx_from_fd, IOMMUFD);

This one looks ok to me. Thanks.

Regards,
Yi Liu