On Tue, Jun 18, 2024 at 01:17:03PM +0200, Clément Léger wrote:
> Since commit 03e471c41d8b ("qemu_init: increase NOFILE soft limit on
> POSIX"), the maximum number of file descriptors that can be opened are
> raised to nofile.rlim_max. On recent debian distro, this yield a maximum
> of 1073741816 file descriptors. Now, when forking to start
> qemu-bridge-helper, this actually calls close() on the full possible file
> descriptor range (more precisely [3 - sysconf(_SC_OPEN_MAX)]) which
> takes a considerable amount of time. In order to reduce that time,
> factorize existing code to close all open files descriptors in a new
> qemu_close_all_open_fd() function. This function uses various methods
> to close all the open file descriptors ranging from the most efficient
> one to the least one. It also accepts an ordered array of file
> descriptors that should not be closed since this is required by the
> callers that calls it after forking.
>
> Signed-off-by: Clément Léger <cle...@rivosinc.com>
>
> ----
>
> v2:
> - Factorize async_teardown.c close_fds implementation as well as tap.c ones
> - Apply checkpatch
> - v1:
> https://lore.kernel.org/qemu-devel/20240617162520.4045016-1-cle...@rivosinc.com/
>
> ---
> include/qemu/osdep.h | 8 +++
> net/tap.c | 31 ++++++-----
> system/async-teardown.c | 37 +------------
> util/osdep.c | 115 ++++++++++++++++++++++++++++++++++++++++
> 4 files changed, 141 insertions(+), 50 deletions(-)
>
> diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
> index f61edcfdc2..9369a97d3d 100644
> --- a/include/qemu/osdep.h
> +++ b/include/qemu/osdep.h
> @@ -755,6 +755,14 @@ static inline void qemu_reset_optind(void)
>
> int qemu_fdatasync(int fd);
>
> +/**
> + * Close all open file descriptors except the ones supplied in the @skip
> array
> + *
> + * @skip: ordered array of distinct file descriptors that should not be
> closed
> + * @nskip: number of entries in the @skip array.
> + */
> +void qemu_close_all_open_fd(const int *skip, unsigned int nskip);
> +
> /**
> * Sync changes made to the memory mapped file back to the backing
> * storage. For POSIX compliant systems this will fallback
> diff --git a/net/tap.c b/net/tap.c
> index 51f7aec39d..6fc3939078 100644
> --- a/net/tap.c
> +++ b/net/tap.c
> @@ -385,6 +385,21 @@ static TAPState *net_tap_fd_init(NetClientState *peer,
> return s;
> }
>
> +static void close_all_fds_after_fork(int excluded_fd)
> +{
> + const int skip_fd[] = {0, 1, 2, 3, excluded_fd};
> + unsigned int nskip = ARRAY_SIZE(skip_fd);
> +
> + /*
> + * skip_fd must be an ordered array of distinct fds, exclude
> + * excluded_fd if already included in the [0 - 3] range
> + */
> + if (excluded_fd <= 3) {
> + nskip--;
> + }
> + qemu_close_all_open_fd(skip_fd, nskip);
> +}
This is slightly over-indented - 4 space is QEMU normal style.
> diff --git a/util/osdep.c b/util/osdep.c
> index 5d23bbfbec..f3710710e3 100644
> --- a/util/osdep.c
> +++ b/util/osdep.c
> @@ -625,3 +625,118 @@ int qemu_fdatasync(int fd)
> return fsync(fd);
> #endif
> }
> +
> +#ifdef CONFIG_LINUX
> +static bool qemu_close_all_open_fd_proc(const int *skip, unsigned int nskip)
> +{
> + struct dirent *de;
> + int fd, dfd;
> + bool close_fd;
> + DIR *dir;
> + int i;
> +
> + dir = opendir("/proc/self/fd");
> + if (!dir) {
> + /* If /proc is not mounted, there is nothing that can be done. */
> + return false;
> + }
> + /* Avoid closing the directory. */
> + dfd = dirfd(dir);
> +
> + for (de = readdir(dir); de; de = readdir(dir)) {
Don't we need
if (de->d_name[0] == '.') {
continue;
}
otherwise atoi will fail and we'll try to close(0) multiple
times.
> + fd = atoi(de->d_name);
> + close_fd = true;
> + if (fd == dfd) {
> + close_fd = false;
> + } else {
> + for (i = 0; i < nskip; i++) {
> + if (fd == skip[i]) {
> + close_fd = false;
> + break;
> + }
> + }
> + }
> + if (close_fd) {
> + close(fd);
> + }
> + }
> + closedir(dir);
> +
> + return true;
> +}
With regards,
Daniel
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