[PATCH 6/7] Implement multiple-filesystem support for remote targets

Gary Benson
2015-04-16T12:27:22Z

This commit allows GDB to access executables and shared libraries
on remote targets where the inferior and the remote stub do not
share a common filesystem. 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_fs_pid): New static variable.
(remote_hostio_set_fs_deferred): New function.
(remote_hostio_set_filesystem): Likewise.
(remote_hostio_open): Call the above.
(remote_hostio_unlink): Likewise.
(remote_hostio_readlink): Likewise.
(init_remote_ops): Initialize to_fileio_set_fs.
(_initialize_remote): Register new "set/show remote
hostio-setfs-packet" command.
* NEWS: Mention that GDB and gdbserver support attaching to
processes in different mount namespaces on GNU/Linux systems.
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.
---
gdb/ChangeLog | 18 +++++++++++++++
gdb/NEWS | 8 +++++++
gdb/doc/ChangeLog | 6 +++++
gdb/doc/gdb.texinfo | 11 +++++++++
gdb/remote.c | 58 +++++++++++++++++++++++++++++++++++++++++++++++++++
5 files changed, 101 insertions(+), 0 deletions(-)

diff --git a/gdb/NEWS b/gdb/NEWS
index 62cbdcb..a9f05e4 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -42,6 +42,10 @@
(no "set sysroot" or "file" commands are required). See "New remote
packets" below.

+* GDB and gdbserver now support attaching to processes running in
+ different mount namespaces from the debugger on GNU/Linux systems.
+ See "New remote packets" below.
+
* Python Scripting

** gdb.Objfile objects have a new attribute "username",
@@ -116,6 +120,10 @@ 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:
+ Set the filesystem accessed by vFile: packets with filename
+ arguments.
+
* The info record command now shows the recording format and the
branch tracing configuration for the current thread when using
the btrace record target.
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index e7872dd..fc0f4b1 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -19889,6 +19889,10 @@ 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
@@ -37533,6 +37537,13 @@ An empty response indicates that this operation is not recognized.
These are the supported Host I/O operations:

@table @samp
+@item vFile:setfs: @var{pid}
+Set the filesystem accessed by @code{vFile} packets with
+@var{filename} arguments to the filesystem as seen by process
+@var{pid}. If @var{pid} is zero, set the filesystem to that
+seen by the remote stub. Return 0 on success, or -1 if an
+error occurs.
+
@item vFile:open: @var{filename}, @var{flags}, @var{mode}
Open a file at @var{filename} and return a file descriptor for it, or
return -1 if an error occurs. The @var{filename} is a string,
diff --git a/gdb/remote.c b/gdb/remote.c
index 3b2325f..3202871 100644
--- a/gdb/remote.c
+++ b/gdb/remote.c
@@ -367,6 +367,12 @@ 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. */
@@ -409,6 +415,7 @@ 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;
}
@@ -1243,6 +1250,7 @@ enum {
PACKET_Z2,
PACKET_Z3,
PACKET_Z4,
+ PACKET_vFile_setfs,
PACKET_vFile_open,
PACKET_vFile_pread,
PACKET_vFile_pwrite,
@@ -9879,6 +9887,46 @@ remote_hostio_send_command (int command_bytes, int which_packet,
return ret;
}

+/* Process ID of inferior whose filesystem remote_hostio functions
+ that take FILENAME arguments will use. Zero means to use the
+ remote stub's filesystem. */
+
+static int remote_fs_pid = 0;
+
+/* Implementation of to_fileio_set_fs. */
+
+static void
+remote_hostio_set_fs_deferred (struct target_ops *self, int pid)
+{
+ remote_fs_pid = pid;
+}
+
+/* Set the filesystem remote_hostio functions that take FILENAME
+ arguments will use. */
+
+static void
+remote_hostio_set_filesystem (void)
+{
+ struct remote_state *rs = get_remote_state ();
+
+ if (rs->fs_pid == -1 || remote_fs_pid != rs->fs_pid)
+ {
+ char *p = rs->buf;
+ int left = get_remote_packet_size () - 1;
+ int remote_errno;
+ char arg[9];
+
+ remote_buffer_add_string (&p, &left, "vFile:setfs:");
+
+ xsnprintf (arg, sizeof (arg), "%x", remote_fs_pid);
+ remote_buffer_add_string (&p, &left, arg);
+
+ if (remote_hostio_send_command (p - rs->buf, PACKET_vFile_setfs,
+ &remote_errno, NULL, NULL) == 0)
+ rs->fs_pid = remote_fs_pid;
+ }
+}
+
/* Return nonzero if the filesystem accessed by the target_fileio_*
methods is the local filesystem, zero otherwise. */

@@ -9901,6 +9949,8 @@ remote_hostio_open (struct target_ops *self,
char *p = rs->buf;
int left = get_remote_packet_size () - 1;

+ remote_hostio_set_filesystem ();
+
remote_buffer_add_string (&p, &left, "vFile:open:");

remote_buffer_add_bytes (&p, &left, (const gdb_byte *) filename,
@@ -10015,6 +10065,8 @@ remote_hostio_unlink (struct target_ops *self,
char *p = rs->buf;
int left = get_remote_packet_size () - 1;

+ remote_hostio_set_filesystem ();
+
remote_buffer_add_string (&p, &left, "vFile:unlink:");

remote_buffer_add_bytes (&p, &left, (const gdb_byte *) filename,
@@ -10040,6 +10092,8 @@ remote_hostio_readlink (struct target_ops *self,
int read_len;
char *ret;

+ remote_hostio_set_filesystem ();
+
remote_buffer_add_string (&p, &left, "vFile:readlink:");

remote_buffer_add_bytes (&p, &left, (const gdb_byte *) filename,
@@ -11756,6 +11810,7 @@ Specify the serial device it is connected to\n\
remote_ops.to_supports_multi_process = remote_supports_multi_process;
remote_ops.to_supports_disable_randomization
= remote_supports_disable_randomization;
+ remote_ops.to_fileio_set_fs = remote_hostio_set_fs_deferred;
remote_ops.to_filesystem_is_local = remote_filesystem_is_local;
remote_ops.to_fileio_open = remote_hostio_open;
remote_ops.to_fileio_pwrite = remote_hostio_pwrite;
@@ -12322,6 +12377,9 @@ 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);

--
1.7.1