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From 607a59f2922b1261920bae94efe4dc87da18d576 Mon Sep 17 00:00:00 2001
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From: Adam Jackson <ajax@redhat.com>
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Date: Tue, 5 Mar 2019 15:31:51 -0500
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Subject: [PATCH] drisw: Try harder to probe whether MIT-SHM works
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XQueryExtension merely tells you whether the extension exists, it
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doesn't tell you whether you're local enough for it to work.
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XShmQueryVersion is not enough to discover this either, you need to
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provoke the server to do actual work, and if it thinks you're remote it
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will throw BadRequest at you. So send an invalid ShmDetach and use the
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error code to distinguish local from remote.
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Signed-off-by: Adam Jackson <ajax@redhat.com>
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---
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src/glx/drisw_glx.c | 26 ++++++++++++++++++++++----
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1 file changed, 22 insertions(+), 4 deletions(-)
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diff --git a/src/glx/drisw_glx.c b/src/glx/drisw_glx.c
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index c63b097a71a..67698d1c450 100644
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--- a/src/glx/drisw_glx.c
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+++ b/src/glx/drisw_glx.c
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@@ -73,11 +73,10 @@ handle_xerror(Display *dpy, XErrorEvent *event)
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(void) dpy;
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assert(xshm_opcode != -1);
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- if (event->request_code != xshm_opcode ||
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- event->minor_code != X_ShmAttach)
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+ if (event->request_code != xshm_opcode)
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return 0;
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- xshm_error = 1;
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+ xshm_error = event->error_code;
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return 0;
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}
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@@ -826,9 +825,28 @@ driswBindExtensions(struct drisw_screen *psc, const __DRIextension **extensions)
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static int
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check_xshm(Display *dpy)
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{
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+ int (*old_handler)(Display *, XErrorEvent *);
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+
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int ignore;
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+ XShmSegmentInfo info = { 0, };
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+
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+ if (!XQueryExtension(dpy, "MIT-SHM", &xshm_opcode, &ignore, &ignore))
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+ return False;
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+
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+ old_handler = XSetErrorHandler(handle_xerror);
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+ XShmDetach(dpy, &info;;
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+ XSync(dpy, False);
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+ (void) XSetErrorHandler(old_handler);
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- return XQueryExtension(dpy, "MIT-SHM", &xshm_opcode, &ignore, &ignore);
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+ /* BadRequest means we're a remote client. If we were local we'd
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+ * expect BadValue since 'info' has an invalid segment name.
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+ */
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+ if (xshm_error == BadRequest)
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+ return False;
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+
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+ /* reset this as others read it later */
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+ xshm_error = 0;
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+ return True;
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}
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static struct glx_screen *
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--
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2.20.1
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