| Message ID | 1350085772-8755-2-git-send-email-mcgrof@do-not-panic.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Sat, Oct 13, 2012 at 3:33 AM, Laurent Pinchart <laurent.pinchart@ideasonboard.com> wrote: > Hi Luis, > > On Friday 12 October 2012 16:49:31 Luis R. Rodriguez wrote: >> From: "Luis R. Rodriguez" <mcgrof@do-not-panic.com> >> >> The UAPI changes split kernel API and userspace API >> content onto two separate header files. The userspace >> API drm content was moved to include/uapi/drm/ with the >> same file name while kernel specific API content was >> kept under include/drm/ with the same file name. When >> one file was split into two files the kernel header >> includes the uapi header and a UAPI prefix was added to >> the uapi header for its header guard. When there was no >> kernel API content found the uapi header file was the >> only one that was kept and the original guard for the >> header file was kept. In this particular case the >> original users of this header file were not modified >> and the uapi header file is expected to be picked up >> by path. >> >> This may work well at compilation on the kernel but when >> backporting this creates a few complexities. > > Could you please provide more details about those complexities ? Sure, the backported DRM code is as-is code from linux-next. The header search path includes a copy of a few select header files from linux-next, the rest are part of the compat [0] project to help with backporting and the last set are from your own kernel. In this particular case the UAPI effort pushed into include/uapi/drm a few files which are now no longer present in the old include/drm/ location when there was no respective kernel-only APIs exposed. For DRM code that did not use the new uapi/drm/ path for old header includes this means that upon backporting the older kernel's header file would be used obviously leading to a series of compilation failures. By being explicit about the path, as was done with a few other header files, we can suck out DRM code intact from the kernel to be compilable for older kernels. As of the v3.7-rc1 the compat-drivers project [1] will be providing DRM modules. The new UAPI changes broke compilation on compat-drivers when compiling DRM code so to fix this we either patch code taken from the Linux kernel as I have done, force inclusion of a few specific headers files, or use include_next tricks. It turns out that forcing inclusion of -I$(M)/include/uapi as a path search prior to your own kernel's at compilation time did not help. The include_next trick can work as well but that'd mean synching the UAPI files regularly into compat. I'd much prefer to have code intact when possible when backporting so the option I stuck with then was to patch the code directly and then as part of compat-drivers to always copy that day's linux-next UAPI headers into the current directory for compilation. I see no other driver code using the uapi path explicitly though, is that by design? Would it be wrong to be explicit about using a UAPI header alone if no kernel API files exist? [0] https://backports.wiki.kernel.org/index.php/Documentation/compat [1] https://backports.wiki.kernel.org/ Luis
Hi Luis, On Saturday 13 October 2012 10:00:42 Luis R. Rodriguez wrote: > On Sat, Oct 13, 2012 at 3:33 AM, Laurent Pinchart wrote: > > On Friday 12 October 2012 16:49:31 Luis R. Rodriguez wrote: > >> From: "Luis R. Rodriguez" <mcgrof@do-not-panic.com> > >> > >> The UAPI changes split kernel API and userspace API > >> content onto two separate header files. The userspace > >> API drm content was moved to include/uapi/drm/ with the > >> same file name while kernel specific API content was > >> kept under include/drm/ with the same file name. When > >> one file was split into two files the kernel header > >> includes the uapi header and a UAPI prefix was added to > >> the uapi header for its header guard. When there was no > >> kernel API content found the uapi header file was the > >> only one that was kept and the original guard for the > >> header file was kept. In this particular case the > >> original users of this header file were not modified > >> and the uapi header file is expected to be picked up > >> by path. > >> > >> This may work well at compilation on the kernel but when > >> backporting this creates a few complexities. > > > > Could you please provide more details about those complexities ? > > Sure, the backported DRM code is as-is code from linux-next. The > header search path includes a copy of a few select header files from > linux-next, the rest are part of the compat [0] project to help with > backporting and the last set are from your own kernel. In this > particular case the UAPI effort pushed into include/uapi/drm a few > files which are now no longer present in the old include/drm/ location > when there was no respective kernel-only APIs exposed. For DRM code > that did not use the new uapi/drm/ path for old header includes this > means that upon backporting the older kernel's header file would be > used obviously leading to a series of compilation failures. By being > explicit about the path, as was done with a few other header files, we > can suck out DRM code intact from the kernel to be compilable for > older kernels. As of the v3.7-rc1 the compat-drivers project [1] will > be providing DRM modules. The new UAPI changes broke compilation on > compat-drivers when compiling DRM code so to fix this we either patch > code taken from the Linux kernel as I have done, force inclusion of a > few specific headers files, or use include_next tricks. It turns out > that forcing inclusion of -I$(M)/include/uapi as a path search prior > to your own kernel's at compilation time did not help. Shouldn't that be added as a search path *after* include/linux/ instead of before ? > The include_next trick can work as well but that'd mean synching the UAPI > files regularly into compat. I'd much prefer to have code intact when > possible when backporting so the option I stuck with then was to patch > the code directly and then as part of compat-drivers to always copy > that day's linux-next UAPI headers into the current directory for > compilation. I see no other driver code using the uapi path explicitly > though, is that by design? As far as I understand that's by design, yes. Kernel code isn't expected to reference uapi/ headers directly. > Would it be wrong to be explicit about using a UAPI header alone if no > kernel API files exist? I personally don't really like including such "features" in a mainline just for backporting, especially when they go against the spirit of the architecture (the uapi/ split design principles in this case). The way we're dealing with this in the V4L backport tree (http://git.linuxtv.org/media_build.git) is to play with Makefiles, include compatibility headers and, if nothing else can work, maintain backport patches for mainline code. > [0] https://backports.wiki.kernel.org/index.php/Documentation/compat > [1] https://backports.wiki.kernel.org/
On Tue, Oct 16, 2012 at 5:34 AM, Laurent Pinchart <laurent.pinchart@ideasonboard.com> wrote: > Hi Luis, > > On Saturday 13 October 2012 10:00:42 Luis R. Rodriguez wrote: >> On Sat, Oct 13, 2012 at 3:33 AM, Laurent Pinchart wrote: >> > On Friday 12 October 2012 16:49:31 Luis R. Rodriguez wrote: >> >> From: "Luis R. Rodriguez" <mcgrof@do-not-panic.com> >> >> >> >> The UAPI changes split kernel API and userspace API >> >> content onto two separate header files. The userspace >> >> API drm content was moved to include/uapi/drm/ with the >> >> same file name while kernel specific API content was >> >> kept under include/drm/ with the same file name. When >> >> one file was split into two files the kernel header >> >> includes the uapi header and a UAPI prefix was added to >> >> the uapi header for its header guard. When there was no >> >> kernel API content found the uapi header file was the >> >> only one that was kept and the original guard for the >> >> header file was kept. In this particular case the >> >> original users of this header file were not modified >> >> and the uapi header file is expected to be picked up >> >> by path. >> >> >> >> This may work well at compilation on the kernel but when >> >> backporting this creates a few complexities. >> > >> > Could you please provide more details about those complexities ? >> >> Sure, the backported DRM code is as-is code from linux-next. The >> header search path includes a copy of a few select header files from >> linux-next, the rest are part of the compat [0] project to help with >> backporting and the last set are from your own kernel. In this >> particular case the UAPI effort pushed into include/uapi/drm a few >> files which are now no longer present in the old include/drm/ location >> when there was no respective kernel-only APIs exposed. For DRM code >> that did not use the new uapi/drm/ path for old header includes this >> means that upon backporting the older kernel's header file would be >> used obviously leading to a series of compilation failures. By being >> explicit about the path, as was done with a few other header files, we >> can suck out DRM code intact from the kernel to be compilable for >> older kernels. As of the v3.7-rc1 the compat-drivers project [1] will >> be providing DRM modules. The new UAPI changes broke compilation on >> compat-drivers when compiling DRM code so to fix this we either patch >> code taken from the Linux kernel as I have done, force inclusion of a >> few specific headers files, or use include_next tricks. It turns out >> that forcing inclusion of -I$(M)/include/uapi as a path search prior >> to your own kernel's at compilation time did not help. > > Shouldn't that be added as a search path *after* include/linux/ instead of > before ? Ah, therein lies the issue. If backporting no, if backporting you should seek first for your current directory's include/drm/ dir and then uapi, and then only later the older kernel's paths: NOSTDINC_FLAGS := \ -I$(M)/include/ \ -I$(M)/include/drm \ -I$(M)/include/uapi \ -include $(M)/include/linux/compat-2.6.h \ $(CFLAGS) >> The include_next trick can work as well but that'd mean synching the UAPI >> files regularly into compat. I'd much prefer to have code intact when >> possible when backporting so the option I stuck with then was to patch >> the code directly and then as part of compat-drivers to always copy >> that day's linux-next UAPI headers into the current directory for >> compilation. I see no other driver code using the uapi path explicitly >> though, is that by design? > > As far as I understand that's by design, yes. Kernel code isn't expected to > reference uapi/ headers directly. Did the design consider the case where no respective kernel API header file would ever exist? >> Would it be wrong to be explicit about using a UAPI header alone if no >> kernel API files exist? > > I personally don't really like including such "features" in a mainline just > for backporting, Sort of ditto. I haven't yet made a strong case for one particular situation where this would help (but I will in the long run, see blog), but this example should not be considered one. The patch itself should be considered in terms of its merit for clarifying usage and assumptions of uapi. The fact that I came up with it due to issues when backporting is only secondary. > especially when they go against the spirit of the > architecture (the uapi/ split design principles in this case). The patches, pull request, and even lwn article did not cover the intent on architecture so if it was the design objective I'd like to know how that is determined. From the looks of it, this as all scripted and I do wonder if the case where no kernel API header file existed was taken into consideration. > The way we're > dealing with this in the V4L backport tree > (http://git.linuxtv.org/media_build.git) is to play with Makefiles, include > compatibility headers and, if nothing else can work, maintain backport patches > for mainline code. Thanks for the heads up, I can certainly keep these patches as external but when if I see something that typically may be addressed upstream for non-backport purposes I typically post it for review. I can't say I'm still satisfied with the answers. Why would we restrict drivers with direct access to uapi headers, specially when no kernel API header exists? Luis
Luis R. Rodriguez <mcgrof@do-not-panic.com> wrote: > >> The include_next trick can work as well but that'd mean synching the UAPI > >> files regularly into compat. I'd much prefer to have code intact when > >> possible when backporting so the option I stuck with then was to patch > >> the code directly and then as part of compat-drivers to always copy > >> that day's linux-next UAPI headers into the current directory for > >> compilation. I see no other driver code using the uapi path explicitly > >> though, is that by design? > > > > As far as I understand that's by design, yes. Kernel code isn't expected to > > reference uapi/ headers directly. > > Did the design consider the case where no respective kernel API header > file would ever exist? I didn't particularly design it such that kernel .c files couldn't access uapi .h files directly. I did, however, design it so that my scripts wouldn't have to touch any .c files where possible, and certainly I didn't want to have to double up all #includes that refer to KAPI/UAPI split headers. Ideally, I'd've used #include_next in the KAPI file to refer to the UAPI file where both exist, but some people have strong objections to that, so I ended up having to do #include <uapi/...> instead. I also didn't want to rename the asm/, linux/, etc. prefixes as that would mandate changing pretty much every #include in the kernel. For the case where no respective KAPI file exists, it was considered and it is handled. This is done by adding extra -I flags, for example: -I include -I include/uapi so looking for linux/foo.h, say, will look first for include/linux/foo.h and then for include/uapi/linux/foo.h. David
diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c index ef1b221..6486e89 100644 --- a/drivers/gpu/drm/drm_crtc.c +++ b/drivers/gpu/drm/drm_crtc.c @@ -35,7 +35,7 @@ #include <drm/drmP.h> #include <drm/drm_crtc.h> #include <drm/drm_edid.h> -#include <drm/drm_fourcc.h> +#include <uapi/drm/drm_fourcc.h> /* Avoid boilerplate. I'm tired of typing. */ #define DRM_ENUM_NAME_FN(fnname, list) \ diff --git a/drivers/gpu/drm/nouveau/nv04_cursor.c b/drivers/gpu/drm/nouveau/nv04_cursor.c index fe86f0d..7af590f 100644 --- a/drivers/gpu/drm/nouveau/nv04_cursor.c +++ b/drivers/gpu/drm/nouveau/nv04_cursor.c @@ -1,5 +1,5 @@ #include <drm/drmP.h> -#include <drm/drm_mode.h> +#include <uapi/drm/drm_mode.h> #include "nouveau_drm.h" #include "nouveau_reg.h" #include "nouveau_crtc.h" diff --git a/drivers/staging/omapdrm/omap_crtc.c b/drivers/staging/omapdrm/omap_crtc.c index 732f2ad..029c9ec 100644 --- a/drivers/staging/omapdrm/omap_crtc.c +++ b/drivers/staging/omapdrm/omap_crtc.c @@ -19,7 +19,7 @@ #include "omap_drv.h" -#include "drm_mode.h" +#include <uapi/drm/drm_mode.h> #include "drm_crtc.h" #include "drm_crtc_helper.h" diff --git a/include/drm/drmP.h b/include/drm/drmP.h index 3fd8280..9030369 100644 --- a/include/drm/drmP.h +++ b/include/drm/drmP.h @@ -72,8 +72,8 @@ #include <linux/workqueue.h> #include <linux/poll.h> #include <asm/pgalloc.h> -#include <drm/drm.h> -#include <drm/drm_sarea.h> +#include <uapi/drm/drm.h> +#include <uapi/drm/drm_sarea.h> #include <linux/idr.h> diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h index 3fa18b7..1012503 100644 --- a/include/drm/drm_crtc.h +++ b/include/drm/drm_crtc.h @@ -30,9 +30,9 @@ #include <linux/types.h> #include <linux/idr.h> #include <linux/fb.h> -#include <drm/drm_mode.h> -#include <drm/drm_fourcc.h> +#include <uapi/drm/drm_mode.h> +#include <uapi/drm/drm_fourcc.h> struct drm_device; struct drm_mode_set; diff --git a/include/uapi/drm/drm.h b/include/uapi/drm/drm.h index 1e3481e..51ee504 100644 --- a/include/uapi/drm/drm.h +++ b/include/uapi/drm/drm.h @@ -628,7 +628,7 @@ struct drm_prime_handle { __s32 fd; }; -#include <drm/drm_mode.h> +#include <uapi/drm/drm_mode.h> #define DRM_IOCTL_BASE 'd' #define DRM_IO(nr) _IO(DRM_IOCTL_BASE,nr)