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authorDemi Marie Obenour <demiobenour@gmail.com>2022-01-31 20:23:07 +0300
committerJuergen Gross <jgross@suse.com>2022-02-03 10:23:32 +0300
commit164666fa66669d437bdcc8d5f1744a2aee73be41 (patch)
treefbf92095acdeaf34419af1f4501500cb152a4ce6 /include/uapi/xen
parent4564661af6ee321942ec1ab012191d7adedd3e00 (diff)
downloadlinux-164666fa66669d437bdcc8d5f1744a2aee73be41.tar.xz
Improve docs for IOCTL_GNTDEV_MAP_GRANT_REF
--------------cKY3Ggs6VDUCSn4I6iN78sHA Content-Type: multipart/mixed; boundary="------------g0T69ASidFiPhh4eOY4XzIg1" --------------g0T69ASidFiPhh4eOY4XzIg1 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable The current implementation of gntdev guarantees that the first call to IOCTL_GNTDEV_MAP_GRANT_REF will set @index to 0. This is required to use gntdev for Wayland, which is a future desire of Qubes OS. Additionally, requesting zero grants results in an error, but this was not documented either. Document both of these. Signed-off-by: Demi Marie Obenour <demiobenour@gmail.com> Reviewed-by: Juergen Gross <jgross@suse.com> Link: https://lore.kernel.org/r/f66c5a4e-2034-00b5-a635-6983bd999c07@gmail.com Signed-off-by: Juergen Gross <jgross@suse.com>
Diffstat (limited to 'include/uapi/xen')
-rw-r--r--include/uapi/xen/gntdev.h8
1 files changed, 7 insertions, 1 deletions
diff --git a/include/uapi/xen/gntdev.h b/include/uapi/xen/gntdev.h
index 9ac5515b9bc2..7a7145395c09 100644
--- a/include/uapi/xen/gntdev.h
+++ b/include/uapi/xen/gntdev.h
@@ -47,7 +47,13 @@ struct ioctl_gntdev_grant_ref {
/*
* Inserts the grant references into the mapping table of an instance
* of gntdev. N.B. This does not perform the mapping, which is deferred
- * until mmap() is called with @index as the offset.
+ * until mmap() is called with @index as the offset. @index should be
+ * considered opaque to userspace, with one exception: if no grant
+ * references have ever been inserted into the mapping table of this
+ * instance, @index will be set to 0. This is necessary to use gntdev
+ * with userspace APIs that expect a file descriptor that can be
+ * mmap()'d at offset 0, such as Wayland. If @count is set to 0, this
+ * ioctl will fail.
*/
#define IOCTL_GNTDEV_MAP_GRANT_REF \
_IOC(_IOC_NONE, 'G', 0, sizeof(struct ioctl_gntdev_map_grant_ref))