shm: Pick the shm dir at run time, not build time.

Prodding the builder's filesystem for tmp dirs doesn't necessarily
tell you anything about what the actual host's filesystem is going to
look like, so we should just try the dirs at runtime.

Signed-off-by: Eric Anholt <eric@anholt.net>
(cherry picked from commit 19f6cb570becbc4e355807199c6e251fc7935132)

4 files changed, 29 insertions, 70 deletions

diff --git a/Xext/shm.c b/Xext/shm.c
index ed43b9202..2739a59e7 100644
--- a/Xext/shm.c
+++ b/Xext/shm.c
@@ -1194,36 +1194,46 @@ ProcShmAttachFd(ClientPtr client)
 static int
 shm_tmpfile(void)
 {
-#ifdef SHMDIR
+    const char *shmdirs[] = {
+        "/run/shm",
+        "/var/tmp",
+        "/tmp",
+    };
     int	fd;
-    char	template[] = SHMDIR "/shmfd-XXXXXX";
+
 #ifdef O_TMPFILE
-    fd = open(SHMDIR, O_TMPFILE|O_RDWR|O_CLOEXEC|O_EXCL, 0666);
-    if (fd >= 0) {
-        DebugF ("Using O_TMPFILE\n");
-        return fd;
+    for (int i = 0; i < ARRAY_SIZE(shmdirs); i++) {
+        fd = open(shmdirs[i], O_TMPFILE|O_RDWR|O_CLOEXEC|O_EXCL, 0666);
+        if (fd >= 0) {
+            DebugF ("Using O_TMPFILE\n");
+            return fd;
+        }
     }
     ErrorF ("Not using O_TMPFILE\n");
 #endif
+
+    for (int i = 0; i < ARRAY_SIZE(shmdirs); i++) {
+        char template[PATH_MAX];
+        snprintf(template, ARRAY_SIZE(template), "%s/shmfd-XXXXXX", shmdirs[i]);
 #ifdef HAVE_MKOSTEMP
-    fd = mkostemp(template, O_CLOEXEC);
+        fd = mkostemp(template, O_CLOEXEC);
 #else
-    fd = mkstemp(template);
+        fd = mkstemp(template);
 #endif
-    if (fd < 0)
-        return -1;
-    unlink(template);
+        if (fd < 0)
+            continue;
+        unlink(template);
 #ifndef HAVE_MKOSTEMP
-    int flags = fcntl(fd, F_GETFD);
-    if (flags != -1) {
-        flags |= FD_CLOEXEC;
-        (void) fcntl(fd, F_SETFD, &flags);
-    }
+        int flags = fcntl(fd, F_GETFD);
+        if (flags != -1) {
+            flags |= FD_CLOEXEC;
+            (void) fcntl(fd, F_SETFD, &flags);
+        }
 #endif
-    return fd;
-#else
+        return fd;
+    }
+
     return -1;
-#endif
 }
 
 static int
diff --git a/configure.ac b/configure.ac
index af16b0afb..93587b500 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1122,49 +1122,6 @@ case "$DRI2,$HAVE_DRI2PROTO" in
 esac
 AM_CONDITIONAL(DRI2, test "x$DRI2" = xyes)
 
-dnl
-dnl Locate a suitable tmp file system for creating shared memeory files
-dnl
-
-AC_ARG_WITH(shared-memory-dir, AS_HELP_STRING([--with-shared-memory-dir=PATH], [Path to directory in a world-writable temporary directory for anonymous shared memory (default: auto)]),
-[],
-[with_shared_memory_dir=yes])
-
-shmdirs="/run/shm /var/tmp /tmp"
-
-case x"$with_shared_memory_dir" in
-xyes)
-	for dir in $shmdirs; do
-		case x"$with_shared_memory_dir" in
-		xyes)
-			echo Checking temp dir "$dir"
-			if test -d "$dir"; then
-				with_shared_memory_dir="$dir"
-			fi
-			;;
-		esac
-	done
-	;;
-x/*)
-	;;
-xno)
-	;;
-*)
-	AC_MSG_ERROR([Invalid directory specified for --with-shared-memory-dir: $with_shared_memory_dir])
-	;;
-esac
-
-case x"$with_shared_memory_dir" in
-xyes)
-	AC_MSG_ERROR([No directory found for shared memory temp files.])
-	;;
-xno)
-	;;
-*)
-	AC_DEFINE_UNQUOTED(SHMDIR, ["$with_shared_memory_dir"], [Directory for shared memory temp files])
-	;;
-esac
-
 AC_ARG_ENABLE(xtrans-send-fds,	AS_HELP_STRING([--disable-xtrans-send-fds], [Use Xtrans support for fd passing (default: auto)]), [XTRANS_SEND_FDS=$enableval], [XTRANS_SEND_FDS=auto])
 
 case "x$XTRANS_SEND_FDS" in
diff --git a/include/dix-config.h.in b/include/dix-config.h.in
index c64321ef1..197ed21d2 100644
--- a/include/dix-config.h.in
+++ b/include/dix-config.h.in
@@ -458,9 +458,6 @@
 /* Wrap SIGBUS to catch MIT-SHM faults */
 #undef BUSFAULT
 
-/* Directory for shared memory temp files */
-#undef SHMDIR
-
 /* Don't let Xdefs.h define 'pointer' */
 #define _XTYPEDEF_POINTER       1
 
diff --git a/include/meson.build b/include/meson.build
index dfca3c340..1e2c7d9ef 100644
--- a/include/meson.build
+++ b/include/meson.build
@@ -70,11 +70,6 @@ conf_data.set('SYSTEMD_LOGIND', build_systemd_logind)
 conf_data.set('NEED_DBUS', build_systemd_logind or build_hal)
 conf_data.set('CONFIG_WSCONS', host_machine.system() == 'openbsd')
 
-# XXX: SHMDIR is weird in autoconf, probing the build system for
-# various tmp directories.  Could we replace it with C code at runtime
-# that just uses whatever directory works?
-conf_data.set_quoted('SHMDIR', '/tmp')
-
 conf_data.set('HAVE_XSHMFENCE', xshmfence_dep.found())
 conf_data.set('WITH_LIBDRM', libdrm_dep.found())
 conf_data.set('GLAMOR_HAS_EGL_QUERY_DMABUF',