[PATCH xserver 7/7] modesetting: Allow a DRM fd to be passed through XF86_VIDEO_MODESETTING_FD

[Keith Packard]

This lets an application open a suitable DRM device and pass the file
descriptor to the mode setting driver through an environment variable.

There's a companion application, xlease, which creates a DRM master by
leasing an output from another X server. That is available at

	git clone git://people.freedesktop.org/~keithp/xlease

Signed-off-by: Keith Packard <keithp at keithp.com>
---
 hw/xfree86/drivers/modesetting/driver.c | 29 ++++++++++++++++++++++++++++-
 hw/xfree86/drivers/modesetting/driver.h |  1 +
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/hw/xfree86/drivers/modesetting/driver.c b/hw/xfree86/drivers/modesetting/driver.c
index 577559ea6..074872e97 100644
--- a/hw/xfree86/drivers/modesetting/driver.c
+++ b/hw/xfree86/drivers/modesetting/driver.c
@@ -194,11 +194,28 @@ modesettingEntPtr ms_ent_priv(ScrnInfoPtr scrn)
     return pPriv->ptr;
 }
 
+static int
+get_passed_fd(void)
+{
+    char *fdstr = getenv("XF86_VIDEO_MODESETTING_FD");
+
+    if (fdstr) {
+        char *endptr;
+        int fd = strtol(fdstr, &endptr, 10);
+        if (endptr != fdstr && *endptr == '\0')
+            return dup(fd);
+    }
+    return -1;
+}
+
 static int
 open_hw(const char *dev)
 {
     int fd;
 
+    if ((fd = get_passed_fd()) >= 0)
+        return fd;
+
     if (dev)
         fd = open(dev, O_RDWR, 0);
     else {
@@ -822,6 +839,12 @@ ms_get_drm_master_fd(ScrnInfoPtr pScrn)
         return TRUE;
     }
 
+    ms->fd_passed = FALSE;
+    if ((ms->fd = get_passed_fd()) >= 0) {
+        ms->fd_passed = TRUE;
+        return TRUE;
+    }
+
 #ifdef XSERVER_PLATFORM_BUS
     if (pEnt->location.type == BUS_PLATFORM) {
         if (pEnt->location.id.plat->flags & XF86_PDEV_SERVER_FD)
@@ -1494,6 +1517,9 @@ SetMaster(ScrnInfoPtr pScrn)
         (ms->pEnt->location.id.plat->flags & XF86_PDEV_SERVER_FD))
         return TRUE;
 
+    if (ms->fd_passed)
+        return TRUE;
+
     ret = drmSetMaster(ms->fd);
     if (ret)
         xf86DrvMsg(pScrn->scrnIndex, X_ERROR, "drmSetMaster failed: %s\n",
@@ -1745,7 +1771,8 @@ LeaveVT(ScrnInfoPtr pScrn)
         (ms->pEnt->location.id.plat->flags & XF86_PDEV_SERVER_FD))
         return;
 
-    drmDropMaster(ms->fd);
+    if (!ms->fd_passed)
+        drmDropMaster(ms->fd);
 }
 
 /*
diff --git a/hw/xfree86/drivers/modesetting/driver.h b/hw/xfree86/drivers/modesetting/driver.h
index fe835918b..6be51e01b 100644
--- a/hw/xfree86/drivers/modesetting/driver.h
+++ b/hw/xfree86/drivers/modesetting/driver.h
@@ -84,6 +84,7 @@ struct ms_drm_queue {
 
 typedef struct _modesettingRec {
     int fd;
+    Bool fd_passed;
 
     int Chipset;
     EntityInfoPtr pEnt;
-- 
2.15.1