Re: [PATCHv3 08/13] scripts/gdb: Add mount point list command

[Kieran Bingham]

On 13/03/16 16:34, Jan Kiszka wrote:
> On 2016-03-03 12:41, 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.
>>
>> Optionally, a user can specify a PID to list from that process'
>> namespace
>>
>> Signed-off-by: Kieran Bingham <kieran.bingham@xxxxxxxxxx>
>>
>> ---
>> Changes from v1:
>>  - Updated to use LX_ constant macros
>>  - Adjusted for new list_for_each_item() function
>>  - Removed unnecessary Null check in vfs['mnt_parent']
>>    - Tested and not needed. It probably occurred in early testing
>>      with a bad iterator
>>
>> Changes since v2:
>>  - dentry path helper moved to utils module
>> ---
>>  scripts/gdb/linux/constants.py.in | 21 +++++++++
>>  scripts/gdb/linux/proc.py         | 99 +++++++++++++++++++++++++++++++++++++++
>>  2 files changed, 120 insertions(+)
>>
>> diff --git a/scripts/gdb/linux/constants.py.in b/scripts/gdb/linux/constants.py.in
>> index 79d9d0092452..57213ad8cf75 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)
>>  
>> @@ -30,3 +34,20 @@
>>  <!-- end-c-headers -->
>>  
>>  import gdb
>> +
>> +/* linux/fs.h */
>> +LX_VALUE(MS_RDONLY)
>> +LX_VALUE(MS_SYNCHRONOUS)
>> +LX_VALUE(MS_MANDLOCK)
>> +LX_VALUE(MS_DIRSYNC)
>> +LX_VALUE(MS_NOATIME)
>> +LX_VALUE(MS_NODIRATIME)
>> +
>> +/* linux/mount.h */
>> +LX_VALUE(MNT_NOSUID)
>> +LX_VALUE(MNT_NODEV)
>> +LX_VALUE(MNT_NOEXEC)
>> +LX_VALUE(MNT_NOATIME)
>> +LX_VALUE(MNT_NODIRATIME)
>> +LX_VALUE(MNT_RELATIME)
>> +
>> diff --git a/scripts/gdb/linux/proc.py b/scripts/gdb/linux/proc.py
>> index d855b2fd9a06..115f20b07a54 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 +100,98 @@ Equivalent to cat /proc/ioports on a running target"""
>>          return show_lx_resources("ioport_resource")
>>  
>>  LxIOPorts()
>> +
>> +
>> +# Mount namespace viewer
>> +#  /proc/mounts
>> +
>> +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.list_for_each_entry(
>> +                                namespace['list'], mount_ptr_type, "mnt_list"):
> 
> pep8 and /me prefer
> 
> for vfs in lists.list_for_each_entry(namespace['list'],
>                                      mount_ptr_type, "mnt_list"):

Ack. No problem.

Did pep8 tool generate a warning here? (Just wondering if this is
another instance of my tool behaving differently)

> 
>> +            devname = vfs['mnt_devname'].string()
>> +            devname = devname if devname else "none"
>> +
>> +            pathname = ""
>> +            parent = vfs
>> +            while True:
>> +                mntpoint = parent['mnt_mountpoint']
>> +                pathname = utils.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()
>>
> 
> This doesn't list all parameters of a mount. Can this be fixed easily?

Not easily I'm afraid: The comment at the top was hoping to highlight this:

>> +    # 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.

Each VFS can call into an extra hook to provide extra option
information. We would need to duplicate each of those implementations :(

> 
> I also noticed that this script lists rootfs, /proc/mounts
> interestingly not. Do you know why?

That is somewhat intriguing! - No, not yet - I did some digging and
haven't come up with a clear answer yet. I'll let you know when I find out!

Kieran

> 
> Jan
>