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

[Jan Kiszka]

Hi Kieran,

just a couple of quick comments:

On 2016-01-20 12:15, Kieran Bingham wrote:
> 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.

current_task? See LxCurrentFunc, could be factored out if usable. Or
what are you looking for?

> 
> 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?

Need to look into this.

> 
> 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.

Maybe we can generate python files with the required constants from the
C headers during build? Similar to asm-offsets.c stuff.

> 
> 
>  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()
> 

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