Re: [PATCH v4 0/6] net/tap: Fix QEMU frozen issue when the maximum number of file descriptors is very large

[Jason Wang]

On Sun, Jul 9, 2023 at 11:48 PM Bin Meng <bmeng.cn@gmail.com> wrote:
>
> On Wed, Jun 28, 2023 at 11:29 PM Bin Meng <bmeng@tinylab.org> wrote:
> >
> >
> > Current codes using a brute-force traversal of all file descriptors
> > do not scale on a system where the maximum number of file descriptors
> > is set to a very large value (e.g.: in a Docker container of Manjaro
> > distribution it is set to 1073741816). QEMU just looks frozen during
> > start-up.
> >
> > The close-on-exec flag (O_CLOEXEC) was introduced since Linux kernel
> > 2.6.23, FreeBSD 8.3, OpenBSD 5.0, Solaris 11. While it's true QEMU
> > doesn't need to manually close the fds for child process as the proper
> > O_CLOEXEC flag should have been set properly on files with its own
> > codes, QEMU uses a huge number of 3rd party libraries and we don't
> > trust them to reliably be using O_CLOEXEC on everything they open.
> >
> > Modern Linux and BSDs have the close_range() call we can use to do the
> > job, and on Linux we have one more way to walk through /proc/self/fd
> > to complete the task efficiently, which is what qemu_close_range()
> > does, a new API we add in util/osdep.c.
> >
> > V1 link: 
> > https://lore.kernel.org/qemu-devel/20230406112041.798585-1-bmeng@tinylab.org/
> >
> > Changes in v4:
> > - add 'first > last' check logic
> > - reorder the ifdefs logic
> > - change i to unsigned int type
> > - use qemu_strtoi() instead of atoi()
> > - limit last upper value to sysconf(_SC_OPEN_MAX) - 1
> > - call sysconf directly instead of using a variable
> > - put fd on its own line
> >
> > Changes in v3:
> > - fix win32 build failure
> > - limit the last_fd of qemu_close_range() to sysconf(_SC_OPEN_MAX)
> >
> > Changes in v2:
> > - new patch: "tests/tcg/cris: Fix the coding style"
> > - new patch: "tests/tcg/cris: Correct the off-by-one error"
> > - new patch: "util/async-teardown: Fall back to close fds one by one"
> > - new patch: "util/osdep: Introduce qemu_close_range()"
> > - new patch: "util/async-teardown: Use qemu_close_range() to close fds"
> > - Change to use qemu_close_range() to close fds for child process 
> > efficiently
> > - v1 link: 
> > https://lore.kernel.org/qemu-devel/20230406112041.798585-1-bmeng@tinylab.org/
> >
> > Bin Meng (4):
> >   tests/tcg/cris: Fix the coding style
> >   tests/tcg/cris: Correct the off-by-one error
> >   util/async-teardown: Fall back to close fds one by one
> >   util/osdep: Introduce qemu_close_range()
> >
> > Zhangjin Wu (2):
> >   util/async-teardown: Use qemu_close_range() to close fds
> >   net: tap: Use qemu_close_range() to close fds
> >
>
> Ping for 8.1?

Queued.

Thanks