|
NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | NOTES | SEE ALSO | COLOPHON |
SD_EVENT_ADD_CHILD(3) sd_event_add_child SD_EVENT_ADD_CHILD(3)
sd_event_add_child, sd_event_add_child_pidfd,
sd_event_source_get_child_pid, sd_event_source_get_child_pidfd,
sd_event_source_get_child_pidfd_own,
sd_event_source_set_child_pidfd_own,
sd_event_source_get_child_process_own,
sd_event_source_set_child_process_own,
sd_event_source_send_child_signal, sd_event_child_handler_t - Add a
child process state change event source to an event loop
#include <systemd/sd-event.h>
typedef struct sd_event_source sd_event_source;
typedef int (*sd_event_child_handler_t)(sd_event_source *s,
const siginfo_t *si,
void *userdata);
int sd_event_add_child(sd_event *event, sd_event_source **source,
pid_t pid, int options,
sd_event_child_handler_t handler,
void *userdata);
int sd_event_add_child_pidfd(sd_event *event,
sd_event_source **source, int pidfd,
int options,
sd_event_child_handler_t handler,
void *userdata);
int sd_event_source_get_child_pid(sd_event_source *source,
pid_t *pid);
int sd_event_source_get_child_pidfd(sd_event_source *source);
int sd_event_source_get_child_pidfd_own(sd_event_source *source);
int sd_event_source_set_child_pidfd_own(sd_event_source *source,
int own);
int sd_event_source_get_child_process_own(sd_event_source *source);
int sd_event_source_set_child_process_own(sd_event_source *source,
int own);
int sd_event_source_send_child_signal(sd_event_source *source,
int sig, const siginfo_t *info,
unsigned flags);
sd_event_add_child() adds a new child process state change event
source to an event loop. The event loop object is specified in the
event parameter, the event source object is returned in the source
parameter. The pid parameter specifies the PID of the process to
watch, which must be a direct child process of the invoking process.
The handler must reference a function to call when the process
changes state. The handler function will be passed the userdata
pointer, which may be chosen freely by the caller. The handler also
receives a pointer to a siginfo_t structure containing information
about the child process event. The options parameter determines which
state changes will be watched for. It must contain an OR-ed mask of
WEXITED (watch for the child process terminating), WSTOPPED (watch
for the child process being stopped by a signal), and WCONTINUED
(watch for the child process being resumed by a signal). See
waitid(2) for further information.
Only a single handler may be installed for a specific child process.
The handler is enabled for a single event (SD_EVENT_ONESHOT), but
this may be changed with sd_event_source_set_enabled(3). If the
handler function returns a negative error code, it will be disabled
after the invocation, even if the SD_EVENT_ON mode was requested
before.
To destroy an event source object use sd_event_source_unref(3), but
note that the event source is only removed from the event loop when
all references to the event source are dropped. To make sure an event
source does not fire anymore, even when there's still a reference to
it kept, consider setting the event source to SD_EVENT_OFF with
sd_event_source_set_enabled(3).
The SIGCHLD signal must be blocked in all threads before this
function is called (using sigprocmask(2) or pthread_sigmask(3)).
If the second parameter of sd_event_add_child() is passed as NULL no
reference to the event source object is returned. In this case the
event source is considered "floating", and will be destroyed
implicitly when the event loop itself is destroyed.
Note that the handler function is invoked at a time where the child
process is not reaped yet (and thus still is exposed as a zombie
process by the kernel). However, the child will be reaped
automatically after the function returns. Child processes for which
no child process state change event sources are installed will not be
reaped by the event loop implementation.
If both a child process state change event source and a SIGCHLD
signal event source is installed in the same event loop, the
configured event source priorities decide which event source is
dispatched first. If the signal handler is processed first, it should
leave the child processes for which child process state change event
sources are installed unreaped.
sd_event_add_child_pidfd() is similar to sd_event_add_child() but
takes a file descriptor referencing the process ("pidfd") instead of
the numeric PID. A suitable file descriptor may be acquired via
pidfd_open(2) and related calls. The passed file descriptor is not
closed when the event source is freed again, unless
sd_event_source_set_child_pidfd_own() is used to turn this behaviour
on. Note that regardless which of sd_event_add_child() and
sd_event_add_child_pidfd() is used for allocating an event source,
the watched process has to be a direct child process of the invoking
process. Also in both cases SIGCHLD has to be blocked in the invoking
process.
sd_event_source_get_child_pid() retrieves the configured PID of a
child process state change event source created previously with
sd_event_add_child(). It takes the event source object as the source
parameter and a pointer to a pid_t variable to return the process ID
in.
sd_event_source_get_child_pidfd() retrieves the file descriptor
referencing the watched process ("pidfd") if this functionality is
available. On kernels that support the concept the event loop will
make use of pidfds to watch child processes, regardless if the
individual event sources are allocated via sd_event_add_child() or
sd_event_add_child_pidfd(). If the latter call was used to allocate
the event source, this function returns the file descriptor used for
allocation. On kernels that do not support the pidfd concept this
function will fail with EOPNOTSUPP. This call takes the event source
object as the source parameter and returns the numeric file
descriptor.
sd_event_source_get_child_pidfd_own() may be used to query whether
the pidfd the event source encapsulates shall be closed when the
event source is freed. This function returns zero if the pidfd shall
be left open, and positive if it shall be closed automatically. By
default this setting defaults to on if the event source was allocated
via sd_event_add_child() and off if it was allocated via
sd_event_add_child_pidfd(). The sd_event_source_set_child_pidfd_own()
function may be used to change the setting and takes a boolean
parameter with the new setting.
sd_event_source_get_child_process_own() may be used to query whether
the process the event source watches shall be killed (with SIGKILL)
and reaped when the event source is freed. This function returns zero
if the process shell be left running, and positive if it shall be
killed and reaped automatically. By default this setting defaults to
off. The sd_event_source_set_child_process_own() function may be used
to change the setting and takes a boolean parameter with the new
setting. Note that currently if the calling process is terminated
abnormally the watched process might survive even thought the event
source ceases to exist. This behaviour might change eventually.
sd_event_source_send_child_signal() may be used to send a UNIX signal
to the watched process. If the pidfd concept is supported in the
kernel, this is implemented via pidfd_send_signal(2) and otherwise
via rt_sigqueueinfo(2) (or via kill(2) in case info is NULL). The
specified parameters match those of these underlying system calls,
except that the info is never modified (and is thus declared
constant). Like for the underlying system calls, the flags parameter
currently must be zero.
On success, these functions return 0 or a positive integer. On
failure, they return a negative errno-style error code.
Errors
Returned errors may indicate the following problems:
-ENOMEM
Not enough memory to allocate an object.
-EINVAL
An invalid argument has been passed. This includes specifying an
empty mask in options or a mask which contains values different
than a combination of WEXITED, WSTOPPED, and WCONTINUED.
-EBUSY
A handler is already installed for this child process, or SIGCHLD
is not blocked.
-ESTALE
The event loop is already terminated.
-ECHILD
The event loop has been created in a different process.
-EDOM
The passed event source is not a child process event source.
-EOPNOTSUPP
A pidfd was requested but the kernel does not support this
concept.
These APIs are implemented as a shared library, which can be compiled
and linked to with the libsystemd pkg-config(1) file.
systemd(1), sd-event(3), sd_event_new(3), sd_event_now(3),
sd_event_add_io(3), sd_event_add_time(3), sd_event_add_signal(3),
sd_event_add_inotify(3), sd_event_add_defer(3),
sd_event_source_set_enabled(3), sd_event_source_set_priority(3),
sd_event_source_set_userdata(3), sd_event_source_set_description(3),
sd_event_source_set_floating(3), waitid(2), sigprocmask(2),
pthread_sigmask(3), pidfd_open(2), pidfd_send_signal(2),
rt_sigqueueinfo(2), kill(2)
This page is part of the systemd (systemd system and service manager)
project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a bug
report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩. This
page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2020-08-13. (At that
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more up-to-date source for the page, or you have corrections or
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of the original manual page), send a mail to man-pages@man7.org
systemd 246 SD_EVENT_ADD_CHILD(3)
Pages that refer to this page: 30-systemd-environment-d-generator(7) , systemd.index(7)