Implement multiple-filesystem support for remote targets

This commit allows GDB to access executables and shared libraries
on remote targets where the remote stub does not share a common
filesystem with the inferior(s).  A new packet "vFile:setfs" is
added to the remote protocol and the three remote hostio functions
with filename arguments are modified to send "vFile:setfs" packets
as necessary.

gdb/ChangeLog:

	* remote.c (struct remote_state) <fs_pid>: New field.
	(new_remote_state): Initialize the above.
	(PACKET_vFile_setfs): New enum value.
	(remote_hostio_set_filesystem): New function.
	(remote_hostio_open): Call the above.
	(remote_hostio_unlink): Likewise.
	(remote_hostio_readlink): Likewise.
	(_initialize_remote): Register new "set/show remote
	hostio-setfs-packet" command.
	* NEWS: Announce new vFile:setfs packet.

gdb/doc/ChangeLog:

	* gdb.texinfo (Remote Configuration): Document the
	"set/show remote hostio-setfs-packet" command.
	(Host I/O Packets): Document the vFile:setfs packet.

5 files changed, 100 insertions, 0 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 2e91c76..8598352 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,18 @@
 2015-06-10  Gary Benson <gbenson@redhat.com>
 
+	* remote.c (struct remote_state) <fs_pid>: New field.
+	(new_remote_state): Initialize the above.
+	(PACKET_vFile_setfs): New enum value.
+	(remote_hostio_set_filesystem): New function.
+	(remote_hostio_open): Call the above.
+	(remote_hostio_unlink): Likewise.
+	(remote_hostio_readlink): Likewise.
+	(_initialize_remote): Register new "set/show remote
+	hostio-setfs-packet" command.
+	* NEWS: Announce new vFile:setfs packet.
+
+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.
diff --git a/gdb/NEWS b/gdb/NEWS
index a309dbf..23f20a7 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -174,6 +174,12 @@ qXfer:exec-file:read
   Return the full absolute name of the file that was executed to
   create a process running on the remote system.
 
+vFile:setfs:
+  Select the filesystem on which vFile: operations with filename
+  arguments will operate.  This is required for GDB to be able to
+  access files on remote targets where the remote stub does not
+  share a common filesystem with the inferior(s).
+
 fork stop reason
   Indicates that a fork system call was executed.
 
diff --git a/gdb/doc/ChangeLog b/gdb/doc/ChangeLog
index a9a8137..9264cfa 100644
--- a/gdb/doc/ChangeLog
+++ b/gdb/doc/ChangeLog
@@ -1,5 +1,11 @@
 2015-06-10  Gary Benson <gbenson@redhat.com>
 
+	* gdb.texinfo (Remote Configuration): Document the
+	"set/show remote hostio-setfs-packet" command.
+	(Host I/O Packets): Document the vFile:setfs packet.
+
+2015-06-10  Gary Benson <gbenson@redhat.com>
+
 	* gdb.texinfo (Debugging Output): Document the "set/show debug
 	linux-namespaces" command.
 
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 4bb092c..f502143 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -19916,6 +19916,10 @@ are:
 @tab @code{vFile:fstat}
 @tab Host I/O
 
+@item @code{hostio-setfs-packet}
+@tab @code{vFile:setfs}
+@tab Host I/O
+
 @item @code{noack-packet}
 @tab @code{QStartNoAckMode}
 @tab Packet acknowledgment
@@ -37742,6 +37746,20 @@ attachment (i.e.@: a trailing semicolon).  The return value is the
 number of target bytes read; the binary attachment may be longer if
 some characters were escaped.
 
+@item vFile:setfs: @var{pid}
+Select the filesystem on which @code{vFile} operations with
+@var{filename} arguments will operate.  This is required for
+@value{GDBN} to be able to access files on remote targets where
+the remote stub does not share a common filesystem with the
+inferior(s).
+
+If @var{pid} is nonzero, select the filesystem as seen by process
+@var{pid}.  If @var{pid} is zero, select the filesystem as seen by
+the remote stub.  Return 0 on success, or -1 if an error occurs.
+If @code{vFile:setfs:} indicates success, the selected filesystem
+remains selected until the next successful @code{vFile:setfs:}
+operation.
+
 @end table
 
 @node Interrupts
diff --git a/gdb/remote.c b/gdb/remote.c
index f8682b4..6dd85fb 100644
--- a/gdb/remote.c
+++ b/gdb/remote.c
@@ -373,6 +373,12 @@ struct remote_state
 
   /* The branch trace configuration.  */
   struct btrace_config btrace_config;
+
+  /* The argument to the last "vFile:setfs:" packet we sent, used
+     to avoid sending repeated unnecessary "vFile:setfs:" packets.
+     Initialized to -1 to indicate that no "vFile:setfs:" packet
+     has yet been sent.  */
+  int fs_pid;
 };
 
 /* Private data that we'll store in (struct thread_info)->private.  */
@@ -415,6 +421,7 @@ new_remote_state (void)
   result->buf = xmalloc (result->buf_size);
   result->remote_traceframe_number = -1;
   result->last_sent_signal = GDB_SIGNAL_0;
+  result->fs_pid = -1;
 
   return result;
 }
@@ -1249,6 +1256,7 @@ enum {
   PACKET_Z2,
   PACKET_Z3,
   PACKET_Z4,
+  PACKET_vFile_setfs,
   PACKET_vFile_open,
   PACKET_vFile_pread,
   PACKET_vFile_pwrite,
@@ -10213,6 +10221,43 @@ remote_hostio_send_command (int command_bytes, int which_packet,
   return ret;
 }
 
+/* Set the filesystem remote_hostio functions that take FILENAME
+   arguments will use.  Return 0 on success, or -1 if an error
+   occurs (and set *REMOTE_ERRNO).  */
+
+static int
+remote_hostio_set_filesystem (struct inferior *inf, int *remote_errno)
+{
+  struct remote_state *rs = get_remote_state ();
+  int required_pid = (inf == NULL || inf->fake_pid_p) ? 0 : inf->pid;
+  char *p = rs->buf;
+  int left = get_remote_packet_size () - 1;
+  char arg[9];
+  int ret;
+
+  if (packet_support (PACKET_vFile_setfs) == PACKET_DISABLE)
+    return 0;
+
+  if (rs->fs_pid != -1 && required_pid == rs->fs_pid)
+    return 0;
+
+  remote_buffer_add_string (&p, &left, "vFile:setfs:");
+
+  xsnprintf (arg, sizeof (arg), "%x", required_pid);
+  remote_buffer_add_string (&p, &left, arg);
+
+  ret = remote_hostio_send_command (p - rs->buf, PACKET_vFile_setfs,
+				    remote_errno, NULL, NULL);
+
+  if (packet_support (PACKET_vFile_setfs) == PACKET_DISABLE)
+    return 0;
+
+  if (ret == 0)
+    rs->fs_pid = required_pid;
+
+  return ret;
+}
+
 /* Implementation of to_fileio_open.  */
 
 static int
@@ -10224,6 +10269,9 @@ remote_hostio_open (struct target_ops *self,
   char *p = rs->buf;
   int left = get_remote_packet_size () - 1;
 
+  if (remote_hostio_set_filesystem (inf, remote_errno) != 0)
+    return -1;
+
   remote_buffer_add_string (&p, &left, "vFile:open:");
 
   remote_buffer_add_bytes (&p, &left, (const gdb_byte *) filename,
@@ -10333,6 +10381,9 @@ remote_hostio_unlink (struct target_ops *self,
   char *p = rs->buf;
   int left = get_remote_packet_size () - 1;
 
+  if (remote_hostio_set_filesystem (inf, remote_errno) != 0)
+    return -1;
+
   remote_buffer_add_string (&p, &left, "vFile:unlink:");
 
   remote_buffer_add_bytes (&p, &left, (const gdb_byte *) filename,
@@ -10357,6 +10408,9 @@ remote_hostio_readlink (struct target_ops *self,
   int read_len;
   char *ret;
 
+  if (remote_hostio_set_filesystem (inf, remote_errno) != 0)
+    return NULL;
+
   remote_buffer_add_string (&p, &left, "vFile:readlink:");
 
   remote_buffer_add_bytes (&p, &left, (const gdb_byte *) filename,
@@ -12711,6 +12765,9 @@ Show the maximum size of the address (in bits) in a memory packet."), NULL,
   add_packet_config_cmd (&remote_protocol_packets[PACKET_qTStatus],
 			 "qTStatus", "trace-status", 0);
 
+  add_packet_config_cmd (&remote_protocol_packets[PACKET_vFile_setfs],
+			 "vFile:setfs", "hostio-setfs", 0);
+
   add_packet_config_cmd (&remote_protocol_packets[PACKET_vFile_open],
 			 "vFile:open", "hostio-open", 0);