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| author | Demi Marie Obenour <demiobenour@gmail.com> | 2022-01-31 18:23:07 +0100 |
|---|---|---|
| committer | Juergen Gross <jgross@suse.com> | 2022-02-03 08:23:32 +0100 |
| commit | 164666fa66669d437bdcc8d5f1744a2aee73be41 (patch) | |
| tree | fbf92095acdeaf34419af1f4501500cb152a4ce6 | |
| parent | xen: xenbus_dev.h: delete incorrect file name (diff) | |
| download | linux-164666fa66669d437bdcc8d5f1744a2aee73be41.tar.xz linux-164666fa66669d437bdcc8d5f1744a2aee73be41.zip | |
Improve docs for IOCTL_GNTDEV_MAP_GRANT_REF
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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>
| -rw-r--r-- | include/uapi/xen/gntdev.h | 8 |
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)) |