Implement mount namespace support for native Linux targets

This commit allows GDB to access executables and shared libraries
on native Linux targets where GDB and the inferior have different
mount namespaces.

gdb/ChangeLog:

	* linux-nat.c (nat/linux-namespaces.h): New include.
	(fileio.h): Likewise.
	(linux_nat_filesystem_is_local): New function.
	(linux_nat_fileio_pid_of): Likewise.
	(linux_nat_fileio_open): Likewise.
	(linux_nat_fileio_readlink): Likewise.
	(linux_nat_fileio_unlink): Likewise.
	(linux_nat_add_target): Initialize to_filesystem_is_local,
	to_fileio_open, to_fileio_readlink and to_fileio_unlink.
	(_initialize_linux_nat): New "set/show debug linux-namespaces"
	commands.
	* NEWS: Mention new "set/show debug linux-namespaces" commands.

gdb/doc/ChangeLog:

	* gdb.texinfo (Debugging Output): Document the "set/show debug
	linux-namespaces" command.

5 files changed, 143 insertions, 0 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 5cbc8d8..2e91c76 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,20 @@
 2015-06-10  Gary Benson <gbenson@redhat.com>
 
+	* linux-nat.c (nat/linux-namespaces.h): New include.
+	(fileio.h): Likewise.
+	(linux_nat_filesystem_is_local): New function.
+	(linux_nat_fileio_pid_of): Likewise.
+	(linux_nat_fileio_open): Likewise.
+	(linux_nat_fileio_readlink): Likewise.
+	(linux_nat_fileio_unlink): Likewise.
+	(linux_nat_add_target): Initialize to_filesystem_is_local,
+	to_fileio_open, to_fileio_readlink and to_fileio_unlink.
+	(_initialize_linux_nat): New "set/show debug linux-namespaces"
+	commands.
+	* NEWS: Mention new "set/show debug linux-namespaces" commands.
+
+2015-06-10  Gary Benson <gbenson@redhat.com>
+
 	* target.h (struct inferior): New forward declaration.
 	(struct target_ops) <to_filesystem_is_local>: Update comment.
 	(struct target_ops) <to_fileio_open>: New argument inf.
diff --git a/gdb/NEWS b/gdb/NEWS
index 11ccd4a..a309dbf 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -137,6 +137,10 @@ 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 linux-namespaces
+show debug linux-namespaces
+  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/doc/ChangeLog b/gdb/doc/ChangeLog
index 4b2d75a..a9a8137 100644
--- a/gdb/doc/ChangeLog
+++ b/gdb/doc/ChangeLog
@@ -1,3 +1,8 @@
+2015-06-10  Gary Benson <gbenson@redhat.com>
+
+	* gdb.texinfo (Debugging Output): Document the "set/show debug
+	linux-namespaces" command.
+
 2015-06-10  Walfred Tedeschi  <walfred.tedeschi@intel.com>
             Mircea Gherzan  <mircea.gherzan@intel.com>
 
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 9e9138b..4bb092c 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -23502,6 +23502,11 @@ Displays the current state of @value{GDBN} JIT debugging.
 Turns on or off debugging messages from the Linux LWP debug support.
 @item show debug lin-lwp
 Show the current state of Linux LWP debugging messages.
+@item set debug linux-namespaces
+@cindex @sc{gnu}/Linux namespaces debug messages
+Turns on or off debugging messages from the Linux namespaces debug support.
+@item show debug linux-namespaces
+Show the current state of Linux namespaces debugging messages.
 @item set debug mach-o
 @cindex Mach-O symbols processing
 Control display of debugging messages related to Mach-O symbols
diff --git a/gdb/linux-nat.c b/gdb/linux-nat.c
index febee84..88f4e3e 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
@@ -4868,6 +4870,104 @@ 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;
+  mode_t nat_mode;
+  int fd;
+
+  if (fileio_to_host_openflags (flags, &nat_flags) == -1
+      || fileio_to_host_mode (mode, &nat_mode) == -1)
+    {
+      *target_errno = FILEIO_EINVAL;
+      return -1;
+    }
+
+  fd = linux_mntns_open_cloexec (linux_nat_fileio_pid_of (inf),
+				 filename, nat_flags, nat_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)
 {
@@ -4921,6 +5021,11 @@ 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
@@ -5038,6 +5143,15 @@ Enables printf debugging output."),
 			     show_debug_linux_nat,
 			     &setdebuglist, &showdebuglist);
 
+  add_setshow_boolean_cmd ("linux-namespaces", 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);