[mutter] device-pool: Add way to open files read-only

[Marge Bot <marge-bot src gnome org>]

commit b4cf839e87db695f01a179d92c1ff47f134d5b27
Author: Jonas Ådahl <jadahl gmail com>
Date:   Tue Apr 6 17:51:59 2021 +0200

    device-pool: Add way to open files read-only
    
    Will be used by libinput's tablet device led device files.
    
    Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1828>

 src/backends/native/meta-device-pool.c | 10 +++++++++-
 src/backends/native/meta-device-pool.h |  1 +
 2 files changed, 10 insertions(+), 1 deletion(-)
---
diff --git a/src/backends/native/meta-device-pool.c b/src/backends/native/meta-device-pool.c
index 8aa2c194fc..ba1cdbaaad 100644
--- a/src/backends/native/meta-device-pool.c
+++ b/src/backends/native/meta-device-pool.c
@@ -247,9 +247,17 @@ meta_device_pool_open (MetaDevicePool       *pool,
     }
   else
     {
+      int open_flags;
+
+      if (flags & META_DEVICE_FILE_FLAG_READ_ONLY)
+        open_flags = O_RDONLY;
+      else
+        open_flags = O_RDWR;
+      open_flags |= O_CLOEXEC;
+
       do
         {
-          fd = open (path, O_RDWR | O_CLOEXEC);
+          fd = open (path, open_flags);
         }
       while (fd == -1 && errno == EINTR);
 
diff --git a/src/backends/native/meta-device-pool.h b/src/backends/native/meta-device-pool.h
index 5889ac7f17..f37fc7302c 100644
--- a/src/backends/native/meta-device-pool.h
+++ b/src/backends/native/meta-device-pool.h
@@ -27,6 +27,7 @@ typedef enum _MetaDeviceFileFlags
 {
   META_DEVICE_FILE_FLAG_NONE = 0,
   META_DEVICE_FILE_FLAG_TAKE_CONTROL = 1 << 0,
+  META_DEVICE_FILE_FLAG_READ_ONLY = 1 << 1,
 } MetaDeviceFileFlags;
 
 typedef struct _MetaDeviceFile MetaDeviceFile;