#include <string.h>
+#include <fcntl.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+
+#ifdef __linux__
+
+/* We want to support these features of Linux even when building GLib
+ * against older versions of system headers. This will allow us to
+ * 'automatically' start supporting a particular feature when GLib is
+ * used with a newer kernel, without recompile.
+ *
+ * This means that we're not changing functionality of GLib simply based
+ * on the set of headers we happen to compile against...
+ */
+
+#ifndef F_LINUX_SPECIFIC_BASE
+#define F_LINUX_SPECIFIC_BASE 1024
+#endif
+
+#ifndef F_ADD_SEALS
+#define F_ADD_SEALS (F_LINUX_SPECIFIC_BASE + 9)
+#define F_GET_SEALS (F_LINUX_SPECIFIC_BASE + 10)
+
+#define F_SEAL_SEAL 0x0001 /* prevent further seals from being set */
+#define F_SEAL_SHRINK 0x0002 /* prevent file from shrinking */
+#define F_SEAL_GROW 0x0004 /* prevent file from growing */
+#define F_SEAL_WRITE 0x0008 /* prevent writes */
+#endif
+
+#endif
+
/**
* SECTION:gunix
* @title: UNIX-specific utilities and integration
{
return g_unix_fd_add_full (G_PRIORITY_DEFAULT, fd, condition, function, user_data, NULL);
}
+
+/**
+ * g_unix_fd_ensure_zero_copy_safe:
+ * @fd: a file descriptor
+ *
+ * Checks whether @fd can be use in zero-copy mode. On Linux, this checks that
+ * the descriptor is a memfd, created with memfd_create(), and tries to apply
+ * seals to it so that it can be safely consumed by another process. On other
+ * Unix systems, this function will fail.
+ *
+ * Returns: whether the fd is safe to use in zero-copy mode. Sealing of memfds
+ * is required for the @fd to be considered safe. If sealing fails, or
+ * memfds are not available, or the @fd is not a memfd, returns %FALSE
+ *
+ * Since: 2.44
+ **/
+gboolean
+g_unix_fd_ensure_zero_copy_safe (gint fd)
+{
+#ifdef F_GET_SEALS
+ gint seals;
+ const gint IMMUTABLE_SEALS = F_SEAL_WRITE |
+ F_SEAL_SHRINK |
+ F_SEAL_GROW |
+ F_SEAL_SEAL;
+
+ g_return_val_if_fail (fd >= 0, FALSE);
+
+ /* Seal the fd if possible (only on Linux 3.17+, and if the fd was created
+ * with memfd_create()). */
+ seals = fcntl (fd, F_GET_SEALS);
+ if (seals == -1)
+ {
+ g_debug ("Retrieving fd seals failed: %s", g_strerror (errno));
+ return FALSE;
+ }
+
+ /* Seal the fd, if it is not already. */
+ if ((seals & (IMMUTABLE_SEALS)) >= IMMUTABLE_SEALS)
+ {
+ g_debug ("%s", "fd already sealed");
+ }
+ else
+ {
+ gint error;
+
+ error = fcntl (fd, F_ADD_SEALS, IMMUTABLE_SEALS);
+ if (error == -1)
+ {
+ g_debug ("fd sealing failed: %s", g_strerror (errno));
+ return FALSE;
+ }
+ }
+
+ return TRUE;
+#else
+ return FALSE;
+#endif
+}