On 6/17/23 07:36, Bin Meng 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 v3:
> - fix win32 build failure
> - limit the last_fd of qemu_close_range() to sysconf(_SC_OPEN_MAX)
Sorry, I didn't see this and sent some comments against v2.
Though using _SC_OPEN_MAX was one of them, so that's nice. :-)
r~