[PATCH 4/5] scripts/gdb: Add mount point list command

[Kieran Bingham]

lx-mounts will identify current mount points based on the 'init_task'
namespace by default, as we do not yet have a kernel thread list
implementation to select the current running thread.

Optionally, a user can specify a PID to list from that process'
namespace

This is somewhat limited vs the /proc/mounts file, as that calls into
vfs hooks through the s_op functions to obtain extra information.

Signed-off-by: Kieran Bingham <kieran.bingham@xxxxxxxxxx>
---


In this patch, I'm interested in your opinions on coding styles.
Would you prefer to see the function helpers, (dentry_name, info_opts) where
they are, or inside the command as class members? Or perhaps defined in utils?

This also shows where I need to take constant information from the kernel.
In this case, they are simple numerical bitflags, and unlikely to change but
I didn't want to duplicate their values.


 scripts/gdb/linux/constants.py.in |  21 ++++++++
 scripts/gdb/linux/proc.py         | 110 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 131 insertions(+)

diff --git a/scripts/gdb/linux/constants.py.in b/scripts/gdb/linux/constants.py.in
index d84084ac945b..739a15d2e984 100644
--- a/scripts/gdb/linux/constants.py.in
+++ b/scripts/gdb/linux/constants.py.in
@@ -12,7 +12,11 @@
  *
  */
 
+#include <linux/fs.h>
+#include <linux/mount.h>
+
 /* We need to stringify expanded macros so that they can be parsed */
 #define STRING(x) #x
 #define XSTRING(x) STRING(x)
 
@@ -20,3 +24,20 @@
 <!-- end-c-headers -->
 
 import gdb
+
+/* linux/fs.h */
+LX_MS_RDONLY = MS_RDONLY
+LX_MS_SYNCHRONOUS = MS_SYNCHRONOUS
+LX_MS_MANDLOCK = MS_MANDLOCK
+LX_MS_DIRSYNC = MS_DIRSYNC
+LX_MS_NOATIME = MS_NOATIME
+LX_MS_NODIRATIME = MS_NODIRATIME
+
+/* linux/mount.h */
+LX_MNT_NOSUID = MNT_NOSUID
+LX_MNT_NODEV = MNT_NODEV
+LX_MNT_NOEXEC = MNT_NOEXEC
+LX_MNT_NOATIME = MNT_NOATIME
+LX_MNT_NODIRATIME = MNT_NODIRATIME
+LX_MNT_RELATIME = MNT_RELATIME
+
diff --git a/scripts/gdb/linux/proc.py b/scripts/gdb/linux/proc.py
index d855b2fd9a06..b79ce2a33a3d 100644
--- a/scripts/gdb/linux/proc.py
+++ b/scripts/gdb/linux/proc.py
@@ -12,6 +12,10 @@
 #
 
 import gdb
+from linux import constants
+from linux import utils
+from linux import tasks
+from linux import lists
 
 
 class LxCmdLine(gdb.Command):
@@ -96,3 +100,109 @@ Equivalent to cat /proc/ioports on a running target"""
         return show_lx_resources("ioport_resource")
 
 LxIOPorts()
+
+
+# Mount namespace viewer
+#  /proc/mounts
+
+
+def dentry_name(d):
+    if d['d_parent'] == d:
+        return ""
+    p = dentry_name(d['d_parent']) + "/"
+    return p + d['d_iname'].string()
+
+
+def info_opts(lst, opt):
+    opts = ""
+    for key, string in lst.items():
+        if opt & key:
+            opts += string
+    return opts
+
+
+FS_INFO = {constants.LX_MS_SYNCHRONOUS: ",sync",
+           constants.LX_MS_MANDLOCK: ",mand",
+           constants.LX_MS_DIRSYNC: ",dirsync",
+           constants.LX_MS_NOATIME: ",noatime",
+           constants.LX_MS_NODIRATIME: ",nodiratime"}
+
+MNT_INFO = {constants.LX_MNT_NOSUID: ",nosuid",
+            constants.LX_MNT_NODEV: ",nodev",
+            constants.LX_MNT_NOEXEC: ",noexec",
+            constants.LX_MNT_NOATIME: ",noatime",
+            constants.LX_MNT_NODIRATIME: ",nodiratime",
+            constants.LX_MNT_RELATIME: ",relatime"}
+
+mount_type = utils.CachedType("struct mount")
+mount_ptr_type = mount_type.get_type().pointer()
+
+
+class LxMounts(gdb.Command):
+    """Report the VFS mounts of the current process namespace.
+
+Equivalent to cat /proc/mounts on a running target
+An integer value can be supplied to display the mount
+values of that process namespace"""
+
+    def __init__(self):
+        super(LxMounts, self).__init__("lx-mounts", gdb.COMMAND_DATA)
+
+    # Equivalent to proc_namespace.c:show_vfsmnt
+    # However, that has the ability to call into s_op functions
+    # whereas we cannot and must make do with the information we can obtain.
+    def invoke(self, arg, from_tty):
+        argv = gdb.string_to_argv(arg)
+        if len(argv) >= 1:
+            try:
+                pid = int(argv[0])
+            except:
+                raise gdb.GdbError("Provide a PID as integer value")
+        else:
+            pid = 1
+
+        task = tasks.get_task_by_pid(pid)
+        if not task:
+            raise gdb.GdbError("Couldn't find a process with PID {}"
+                               .format(pid))
+
+        namespace = task['nsproxy']['mnt_ns']
+        if not namespace:
+            raise gdb.GdbError("No namespace for current process")
+
+        for vfs in lists.items(mount_ptr_type, "mnt_list", namespace['list']):
+            # There appears to be a null entry at the end of the list...
+            if not vfs['mnt_parent']:
+                break
+
+            devname = vfs['mnt_devname'].string()
+            devname = devname if devname else "none"
+
+            pathname = ""
+            parent = vfs
+            while True:
+                mntpoint = parent['mnt_mountpoint']
+                pathname = dentry_name(mntpoint) + pathname
+                if (parent == parent['mnt_parent']):
+                    break
+                parent = parent['mnt_parent']
+
+            if (pathname == ""):
+                pathname = "/"
+
+            superblock = vfs['mnt']['mnt_sb']
+            fstype = superblock['s_type']['name'].string()
+            s_flags = int(superblock['s_flags'])
+            m_flags = int(vfs['mnt']['mnt_flags'])
+            rd = "ro" if (s_flags & constants.LX_MS_RDONLY) else "rw"
+
+            gdb.write(
+                "{} {} {} {}{}{} 0 0\n"
+                .format(devname,
+                        pathname,
+                        fstype,
+                        rd,
+                        info_opts(FS_INFO, s_flags),
+                        info_opts(MNT_INFO, m_flags)))
+
+LxMounts()
-- 
2.5.0