[6/9,v2] Implement mount namespace support for native Linux targets

diff --git a/gdb/NEWS b/gdb/NEWS
index d463b52..1c0e5ea 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -89,6 +89,10 @@  set|show record btrace bts buffer-size
   The obtained size may differ from the requested size.  Use "info
   record" to see the obtained buffer size.
 
+set debug lin-ns
+show debug lin-ns
+  Control display of debugging info regarding Linux namespaces.
+
 * The command 'thread apply all' can now support new option '-ascending'
   to call its specified command for all threads in ascending order.
 
diff --git a/gdb/linux-nat.c b/gdb/linux-nat.c
index b04aa68..85149a2 100644
--- a/gdb/linux-nat.c
+++ b/gdb/linux-nat.c
@@ -66,6 +66,8 @@ 
 #include "target-descriptions.h"
 #include "filestuff.h"
 #include "objfiles.h"
+#include "nat/linux-namespaces.h"
+#include "fileio.h"
 
 #ifndef SPUFS_MAGIC
 #define SPUFS_MAGIC 0x23c9b64e
@@ -4842,6 +4844,104 @@  linux_nat_core_of_thread (struct target_ops *ops, ptid_t ptid)
   return -1;
 }
 
+/* Implementation of to_filesystem_is_local.  */
+
+static int
+linux_nat_filesystem_is_local (struct target_ops *ops)
+{
+  struct inferior *inf = current_inferior ();
+
+  if (inf->fake_pid_p || inf->pid == 0)
+    return 1;
+
+  return linux_ns_same (inf->pid, LINUX_NS_MNT);
+}
+
+/* Convert the INF argument passed to a to_fileio_* method
+   to a process ID suitable for passing to its corresponding
+   linux_mntns_* function.  If INF is non-NULL then the
+   caller is requesting the filesystem seen by INF.  If INF
+   is NULL then the caller is requesting the filesystem seen
+   by the GDB.  We fall back to GDB's filesystem in the case
+   that INF is non-NULL but its PID is unknown.  */
+
+static pid_t
+linux_nat_fileio_pid_of (struct inferior *inf)
+{
+  if (inf == NULL || inf->fake_pid_p || inf->pid == 0)
+    return getpid ();
+  else
+    return inf->pid;
+}
+
+/* Implementation of to_fileio_open.  */
+
+static int
+linux_nat_fileio_open (struct target_ops *self,
+		       struct inferior *inf, const char *filename,
+		       int flags, int mode, int *target_errno)
+{
+  int nat_flags;
+  int fd;
+
+  if (fileio_to_host_openflags (flags, &nat_flags) == -1)
+    {
+      *target_errno = FILEIO_EINVAL;
+      return -1;
+    }
+
+  /* We do not need to convert MODE, since the fileio protocol
+     uses the standard values.  */
+  fd = linux_mntns_open_cloexec (linux_nat_fileio_pid_of (inf),
+				 filename, nat_flags, mode);
+  if (fd == -1)
+    *target_errno = host_to_fileio_error (errno);
+
+  return fd;
+}
+
+/* Implementation of to_fileio_readlink.  */
+
+static char *
+linux_nat_fileio_readlink (struct target_ops *self,
+			   struct inferior *inf, const char *filename,
+			   int *target_errno)
+{
+  char buf[PATH_MAX];
+  int len;
+  char *ret;
+
+  len = linux_mntns_readlink (linux_nat_fileio_pid_of (inf),
+			      filename, buf, sizeof (buf));
+  if (len < 0)
+    {
+      *target_errno = host_to_fileio_error (errno);
+      return NULL;
+    }
+
+  ret = xmalloc (len + 1);
+  memcpy (ret, buf, len);
+  ret[len] = '\0';
+  return ret;
+}
+
+/* Implementation of to_fileio_unlink.  */
+
+static int
+linux_nat_fileio_unlink (struct target_ops *self,
+			 struct inferior *inf, const char *filename,
+			 int *target_errno)
+{
+  int ret;
+
+  ret = linux_mntns_unlink (linux_nat_fileio_pid_of (inf),
+			    filename);
+  if (ret == -1)
+    *target_errno = host_to_fileio_error (errno);
+
+  return ret;
+}
+
 void
 linux_nat_add_target (struct target_ops *t)
 {
@@ -4895,6 +4995,11 @@  linux_nat_add_target (struct target_ops *t)
 
   t->to_core_of_thread = linux_nat_core_of_thread;
 
+  t->to_filesystem_is_local = linux_nat_filesystem_is_local;
+  t->to_fileio_open = linux_nat_fileio_open;
+  t->to_fileio_readlink = linux_nat_fileio_readlink;
+  t->to_fileio_unlink = linux_nat_fileio_unlink;
+
   /* We don't change the stratum; this target will sit at
      process_stratum and thread_db will set at thread_stratum.  This
      is a little strange, since this is a multi-threaded-capable
@@ -5012,6 +5117,15 @@  Enables printf debugging output."),
 			     show_debug_linux_nat,
 			     &setdebuglist, &showdebuglist);
 
+  add_setshow_boolean_cmd ("lin-ns", class_maintenance,
+			   &debug_linux_namespaces, _("\
+Set debugging of GNU/Linux namespaces module."), _("\
+Show debugging of GNU/Linux namespaces module."), _("\
+Enables printf debugging output."),
+			   NULL,
+			   NULL,
+			   &setdebuglist, &showdebuglist);
+
   /* Save this mask as the default.  */
   sigprocmask (SIG_SETMASK, NULL, &normal_mask);