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

[Jan Kiszka]

On 2016-03-14 15:39, Kieran Bingham wrote:
> 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)

Yep.

> 
>>
>>> +            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.

Sorry, missed this.

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

So these options are not available as string somewhere?

Jan

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