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

[Kieran Bingham]

On 14/03/16 15:05, Jan Kiszka wrote:
> 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.

Ok, well I have updated this locally anyway now.

> 
>>
>>>
>>>> +            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.

np.

> 
>>
>> 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?

Short answer: No. Not generically.

Long answer: (after having dug around last night)

The extra operations are determined through several layers of
indirection, and function pointers which end up then parsing the options
however they like, and printing them through the seq_file interface.

First through the .show_options of the super_operations kernfs_sops
struct, which indirects through kernfs_sop_show_options() to call any
kernfs_syscall_ops->show_options function registered.

Some super_operations structures register generic_show_options() which
will map the dentry_root->d_sb->s_options as a string.

It looks like around 14 filesystems use this generic show options,
However, none of the filesystems I have mounted use this...

Looking at a few of the others, they are free to store their options
however they like. For example reiserfs stores as flags which are then
expanded by their specific _show_options...

Regards

Kieran

> Jan
>