Re: [Qemu-devel] [PATCH] gdb command: qemu aios, qemu aiohandlers

[Fam Zheng <famz@redhat.com>]

On Tue, 10/20 12:05, Dr. David Alan Gilbert (git) wrote:
> From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> 
> Two new gdb commands are added:
> 
>   qemu iohandlers
> 
>      that dumps the list of waiting iohandlers, this is particularly
>      useful for trying to figure out where an incoming migration is
>      blocked.  For 'fd_coroutine_enter' cases we dump a full backtrace.
> 
>   qemu aios
>      that dumps the qemu_aio_context list.

I'd assume "qemu aios" is a command to print the list of AioContext instances
rather than handlers in a particular context (qemu_aio_context). How about
"qemu handlers"?

> 
> This is a rewrite of an earlier version prior to Fam's changes
> to the corresponding structures.
> 
> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> 
>   (gdb) qemu aios
>   ----
>   {pfd = {fd = 12, events = 25, revents = 0}, io_read = 0x5634d4033cc0
>   <qemu_laio_completion_cb>, io_write = 0x0, deleted = 0, opaque =
>   0x5634d601e8b8, node = {le_next = 0x5634d5fd2330, le_prev =
>   0x5634d5fd22a0}}
>   ----
>   {pfd = {fd = 6, events = 25, revents = 0}, io_read = 0x5634d3ff1750
>   <event_notifier_dummy_cb>, io_write = 0x0, deleted = 0, opaque =
>   0x5634d5fd22e8, node = {le_next = 0x0, le_prev = 0x5634d5fe8458}}
>   ----
> 
>   (gdb) qemu iohandlers
>   ----
>   {pfd = {fd = 15, events = 25, revents = 0}, io_read = 0x559a843bd850
>   <fd_coroutine_enter>, io_write = 0x0, deleted = 0, opaque =
>   0x7fef1c5fed30, node = {le_next = 0x559a84e9d180, le_prev =
>   0x559a84e9c6b0}}
>   #0  0x0000559a843bdcf0 in qemu_coroutine_switch
>   (from_=from_@entry=0x559a865fd8e0, to_=to_@entry=0x7fef37774ac8,
>   action=action@entry=COROUTINE_YIELD) at
>   /home/dgilbert/git/qemu-world3/coroutine-ucontext.c:177
>   #1  0x0000559a843bd0d0 in qemu_coroutine_yield () at
>   /home/dgilbert/git/qemu-world3/qemu-coroutine.c:145
>   #2  0x0000559a843bd9c5 in yield_until_fd_readable (fd=15) at
>   /home/dgilbert/git/qemu-world3/qemu-coroutine-io.c:90
>   #3  0x0000559a84362337 in socket_get_buffer (opaque=0x559a862f7a00,
>   buf=0x559a84ea0a70 "", pos=<optimized out>, size=32768) at
>   /home/dgilbert/git/qemu-world3/migration/qemu-file-unix.c:69
>   #4  0x0000559a84360c9c in qemu_fill_buffer (f=0x559a84ea0a40)
>       at /home/dgilbert/git/qemu-world3/migration/qemu-file.c:215
>   #5  0x0000559a84361569 in qemu_peek_byte (f=0x559a84ea0a40, offset=0)
>       at /home/dgilbert/git/qemu-world3/migration/qemu-file.c:448
>   #6  0x0000559a843617d4 in qemu_get_be32 (f=0x559a84ea0a40)
>       at /home/dgilbert/git/qemu-world3/migration/qemu-file.c:461
>   #7  0x0000559a843617d4 in qemu_get_be32 (f=f@entry=0x559a84ea0a40)
>       at /home/dgilbert/git/qemu-world3/migration/qemu-file.c:545
>   #8  0x0000559a84187d92 in qemu_loadvm_state (f=f@entry=0x559a84ea0a40)
>       at /home/dgilbert/git/qemu-world3/migration/savevm.c:1070
>   #9  0x0000559a8435dc42 in process_incoming_migration_co
>   (opaque=0x559a84ea0a40)
>       at /home/dgilbert/git/qemu-world3/migration/migration.c:285
>   #10 0x0000559a843bdd5a in coroutine_trampoline (i0=<optimized out>,
>   i1=<optimized out>)
>       at /home/dgilbert/git/qemu-world3/coroutine-ucontext.c:80
>   #11 0x00007fef2a462f10 in __start_context () at /lib64/libc.so.6
>   #12 0x00007fffb7437b50 in  ()
>   #13 0x0000000000000000 in  ()

This sort of clutters the output, I'm wondering if making the backtrace
optional (only dumped when "qemu iohandlers --backtrace") is better?  It's OK
if you decide to keep this, though.

>   ----
>   {pfd = {fd = 4, events = 25, revents = 0}, io_read = 0x559a843b7800
>   <sigfd_handler>, io_write = 0x0, deleted = 0, opaque = 0x4, node =
>   {le_next = 0x559a84e9c740, le_prev = 0x559a86325498}}
>   ----
>   {pfd = {fd = 5, events = 25, revents = 0}, io_read = 0x559a843ac750
>   <event_notifier_dummy_cb>, io_write = 0x0, deleted = 0, opaque =
>   0x559a84e9c6f8, node = {le_next = 0x0, le_prev = 0x559a84e9d1a8}}
>   ----
> ---
>  scripts/qemu-gdb.py    |  4 +++-
>  scripts/qemugdb/aio.py | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 55 insertions(+), 1 deletion(-)
>  create mode 100644 scripts/qemugdb/aio.py
> 
> diff --git a/scripts/qemu-gdb.py b/scripts/qemu-gdb.py
> index d6f2e5a..99344c7 100644
> --- a/scripts/qemu-gdb.py
> +++ b/scripts/qemu-gdb.py
> @@ -26,7 +26,7 @@ import os, sys
>  
>  sys.path.append(os.path.dirname(__file__))
>  
> -from qemugdb import mtree, coroutine
> +from qemugdb import aio, mtree, coroutine
>  
>  class QemuCommand(gdb.Command):
>      '''Prefix for QEMU debug support commands'''
> @@ -37,6 +37,8 @@ class QemuCommand(gdb.Command):
>  QemuCommand()
>  coroutine.CoroutineCommand()
>  mtree.MtreeCommand()
> +aio.IOhandlersCommand()
> +aio.AIOsCommand()
>  
>  # Default to silently passing through SIGUSR1, because QEMU sends it
>  # to itself a lot.
> diff --git a/scripts/qemugdb/aio.py b/scripts/qemugdb/aio.py
> new file mode 100644
> index 0000000..cda2c37
> --- /dev/null
> +++ b/scripts/qemugdb/aio.py
> @@ -0,0 +1,52 @@
> +#!/usr/bin/python
> +
> +# GDB debugging support: aio/iohandler debug
> +#
> +# Copyright (c) 2015 Red Hat, Inc.
> +#
> +# Author: Dr. David Alan Gilbert <dgilbert@redhat.com>
> +#
> +# This work is licensed under the terms of the GNU GPL, version 2 or
> +# later.  See the COPYING file in the top-level directory.
> +#
> +
> +import gdb
> +from qemugdb import coroutine
> +
> +def isnull(ptr):
> +    return ptr == gdb.Value(0).cast(ptr.type)
> +
> +def dump_aiocontext(context):
> +    '''Display a dump and backtrace for an aiocontext'''
> +    cur = context['aio_handlers']['lh_first']
> +    # Get pointers to functions we're going to process specially
> +    sym_fd_coroutine_enter = gdb.parse_and_eval('fd_coroutine_enter')
> +
> +    while not isnull(cur):
> +        entry = cur.dereference()
> +        gdb.write('----\n%s\n' % entry)
> +        if cur['io_read'] == sym_fd_coroutine_enter:
> +            coptr = (cur['opaque'].cast(gdb.lookup_type('FDYieldUntilData').pointer()))['co']
> +            coptr = coptr.cast(gdb.lookup_type('CoroutineUContext').pointer())
> +            coroutine.bt_jmpbuf(coptr['env']['__jmpbuf'])
> +        cur = cur['node']['le_next'];
> +
> +    gdb.write('----\n')
> +
> +class AIOsCommand(gdb.Command):
> +    '''Display aio handlers'''

Maybe also

s/aio handlers/aio handlers in main loop/

?

> +    def __init__(self):
> +        gdb.Command.__init__(self, 'qemu aios', gdb.COMMAND_DATA,
> +                             gdb.COMPLETE_NONE)
> +
> +    def invoke(self, arg, from_tty):
> +        dump_aiocontext(gdb.parse_and_eval('qemu_aio_context'))
> +
> +class IOhandlersCommand(gdb.Command):
> +    '''Display io handlers'''
> +    def __init__(self):
> +        gdb.Command.__init__(self, 'qemu iohandlers', gdb.COMMAND_DATA,
> +                             gdb.COMPLETE_NONE)
> +
> +    def invoke(self, arg, from_tty):
> +        dump_aiocontext(gdb.parse_and_eval('iohandler_ctx'))
> -- 
> 2.5.0
>