/usr/include/libxl_event.h is in libxen-dev 4.4.1-9+deb8u10.
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* Copyright (C) 2011 Citrix Ltd.
* Author Ian Jackson <ian.jackson@eu.citrix.com>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published
* by the Free Software Foundation; version 2.1 only. with the special
* exception on linking described in file LICENSE.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Lesser General Public License for more details.
*/
#ifndef LIBXL_EVENT_H
#define LIBXL_EVENT_H
#include <libxl.h>
#include <poll.h>
#include <sys/time.h>
/*======================================================================*/
/*
* Domain event handling - getting Xen events from libxl
*
* (Callers inside libxl may not call libxl_event_check or _wait.)
*/
#define LIBXL_EVENTMASK_ALL (~(unsigned long)0)
typedef int libxl_event_predicate(const libxl_event*, void *user);
/* Return value is 0 if the event is unwanted or non-0 if it is.
* Predicates are not allowed to fail.
*/
int libxl_event_check(libxl_ctx *ctx, libxl_event **event_r,
uint64_t typemask,
libxl_event_predicate *predicate, void *predicate_user)
LIBXL_EXTERNAL_CALLERS_ONLY;
/* Searches for an event, already-happened, which matches typemask
* and predicate. predicate==0 matches any event.
* libxl_event_check returns the event, which must then later be
* freed by the caller using libxl_event_free.
*
* Returns ERROR_NOT_READY if no such event has happened.
*/
int libxl_event_wait(libxl_ctx *ctx, libxl_event **event_r,
uint64_t typemask,
libxl_event_predicate *predicate, void *predicate_user)
LIBXL_EXTERNAL_CALLERS_ONLY;
/* Like libxl_event_check but blocks if no suitable events are
* available, until some are. Uses libxl_osevent_beforepoll/
* _afterpoll so may be inefficient if very many domains are being
* handled by a single program.
*/
void libxl_event_free(libxl_ctx *ctx, libxl_event *event);
/* Alternatively or additionally, the application may also use this: */
typedef struct libxl_event_hooks {
uint64_t event_occurs_mask;
void (*event_occurs)(void *user,
#ifndef LIBXL_HAVE_NONCONST_EVENT_OCCURS_EVENT_ARG
const
#endif
libxl_event *event);
void (*disaster)(void *user, libxl_event_type type,
const char *msg, int errnoval);
} libxl_event_hooks;
void libxl_event_register_callbacks(libxl_ctx *ctx,
const libxl_event_hooks *hooks, void *user);
/*
* Arranges that libxl will henceforth call event_occurs for any
* events whose type is set in event_occurs_mask, rather than
* queueing the event for retrieval by libxl_event_check/wait.
* Events whose bit is clear in mask are not affected.
*
* event becomes owned by the application and must be freed, either
* by event_occurs or later.
*
* event_occurs may be NULL if mask is 0.
*
* libxl_event_register_callback also provides a way for libxl to
* report to the application that there was a problem reporting
* events; this can occur due to lack of host memory during event
* handling, or other wholly unrecoverable errors from system calls
* made by libxl. This will not happen for frivolous reasons - only
* if the system, or the Xen components of it, are badly broken.
*
* msg and errnoval will describe the action that libxl was trying
* to do, and type specifies the type of libxl events which may be
* missing. type may be 0 in which case events of all types may be
* missing.
*
* disaster may be NULL. If it is, or if _register_callbacks has
* not been called, errors of this kind are fatal to the entire
* application: libxl will print messages to its logs and to stderr
* and call exit(-1).
*
* If disaster returns, it may be the case that some or all future
* libxl calls will return errors; likewise it may be the case that
* no more events (of the specified type, if applicable) can be
* produced. An application which supplies a disaster function
* should normally react either by exiting, or by (when it has
* returned to its main event loop) shutting down libxl with
* libxl_ctx_free and perhaps trying to restart it with
* libxl_ctx_init.
*
* In any case before calling disaster, libxl will have logged a
* message with level XTL_CRITICAL.
*
* Reentrancy: it IS permitted to call libxl from within
* event_occurs. It is NOT permitted to call libxl from within
* disaster. The event_occurs and disaster callbacks may occur on
* any thread in which the application calls libxl.
*
* libxl_event_register_callbacks may be called as many times, with
* different parameters, as the application likes; the most recent
* call determines the libxl behaviour. However it is NOT safe to
* call _register_callbacks concurrently with, or reentrantly from,
* any other libxl function.
*
* Calls to _register_callbacks do not affect events which have
* already occurred.
*/
/*
* Events are only generated if they have been requested.
* The following functions request the generation of specific events.
*
* Each set of functions for controlling event generation has this form:
*
* typedef struct libxl__evgen_FOO libxl__evgen_FOO;
* int libxl_evenable_FOO(libxl_ctx *ctx, FURTHER PARAMETERS,
* libxl_ev_user user, libxl__evgen_FOO **evgen_out);
* void libxl_evdisable_FOO(libxl_ctx *ctx, libxl__evgen_FOO *evgen);
*
* The evenable function arranges that the events (as described in the
* doc comment for the individual function) will start to be generated
* by libxl. On success, *evgen_out is set to a non-null pointer to
* an opaque struct.
*
* The user value is returned in the generated events and may be
* used by the caller for whatever it likes. The type ev_user is
* guaranteed to be an unsigned integer type which is at least
* as big as uint64_t and is also guaranteed to be big enough to
* contain any intptr_t value.
*
* If it becomes desirable to stop generation of the relevant events,
* or to reclaim the resources in libxl associated with the evgen
* structure, the same evgen value should be passed to the evdisable
* function. However, note that events which occurred prior to the
* evdisable call may still be returned.
*
* The caller may enable identical events more than once. If they do
* so, each actual occurrence will generate several events to be
* returned by libxl_event_check, with the appropriate user value(s).
* Aside from this, each occurrence of each event is returned by
* libxl_event_check exactly once.
*
* An evgen is associated with the libxl_ctx used for its creation.
* After libxl_ctx_free, all corresponding evgen handles become
* invalid and must no longer be passed to evdisable.
*
* Applications should ensure that they eventually retrieve every
* event using libxl_event_check or libxl_event_wait, since events
* which occur but are not retreived by the application will be queued
* inside libxl indefinitely. libxl_event_check/_wait may be O(n)
* where n is the number of queued events which do not match the
* criteria specified in the arguments to check/wait.
*/
typedef struct libxl__evgen_domain_death libxl_evgen_domain_death;
int libxl_evenable_domain_death(libxl_ctx *ctx, uint32_t domid,
libxl_ev_user, libxl_evgen_domain_death **evgen_out);
void libxl_evdisable_domain_death(libxl_ctx *ctx, libxl_evgen_domain_death*);
/* Arranges for the generation of DOMAIN_SHUTDOWN and DOMAIN_DESTROY
* events. A domain which is destroyed before it shuts down
* may generate only a DESTROY event.
*/
typedef struct libxl__evgen_disk_eject libxl_evgen_disk_eject;
int libxl_evenable_disk_eject(libxl_ctx *ctx, uint32_t domid, const char *vdev,
libxl_ev_user, libxl_evgen_disk_eject **evgen_out);
void libxl_evdisable_disk_eject(libxl_ctx *ctx, libxl_evgen_disk_eject*);
/* Arranges for the generation of DISK_EJECT events. A copy of the
* string *vdev will be made for libxl's internal use, and a pointer
* to this (or some other) copy will be returned as the vdev
* member of event.u.
*/
/*======================================================================*/
/*
* OS event handling - passing low-level OS events to libxl
*
* Event-driven programs must use these facilities to allow libxl
* to become aware of readability/writeability of file descriptors
* and the occurrence of timeouts.
*
* There are two approaches available. The first is appropriate for
* simple programs handling reasonably small numbers of domains:
*
* for (;;) {
* libxl_osevent_beforepoll(...)
* poll();
* libxl_osevent_afterpoll(...);
* for (;;) {
* r = libxl_event_check(...);
* if (r==LIBXL_NOT_READY) break;
* if (r) goto error_out;
* do something with the event;
* }
* }
*
* The second approach uses libxl_osevent_register_hooks and is
* suitable for programs which are already using a callback-based
* event library.
*
* An application may freely mix the two styles of interaction.
*
* (Callers inside libxl may not call libxl_osevent_... functions.)
*/
struct pollfd;
/* The caller should provide beforepoll with some space for libxl's
* fds, and tell libxl how much space is available by setting *nfds_io.
* fds points to the start of this space (and fds may be a pointer into
* a larger array, for example, if the application has some fds of
* its own that it is interested in).
*
* On return *nfds_io will in any case have been updated by libxl
* according to how many fds libxl wants to poll on.
*
* If the space was sufficient, libxl fills in fds[0..<new
* *nfds_io>] suitably for poll(2), updates *timeout_upd if needed,
* and returns ok.
*
* If space was insufficient, fds[0..<old *nfds_io>] is undefined on
* return; *nfds_io on return will be greater than the value on
* entry; *timeout_upd may or may not have been updated; and
* libxl_osevent_beforepoll returns ERROR_BUFERFULL. In this case
* the application needs to make more space (enough space for
* *nfds_io struct pollfd) and then call beforepoll again, before
* entering poll(2). Typically this will involve calling realloc.
*
* The application may call beforepoll with fds==NULL and
* *nfds_io==0 in order to find out how much space is needed.
*
* *timeout_upd is as for poll(2): it's in milliseconds, and
* negative values mean no timeout (infinity).
* libxl_osevent_beforepoll will only reduce the timeout, naturally.
*/
int libxl_osevent_beforepoll(libxl_ctx *ctx, int *nfds_io,
struct pollfd *fds, int *timeout_upd,
struct timeval now)
LIBXL_EXTERNAL_CALLERS_ONLY;
/* nfds and fds[0..nfds] must be from the most recent call to
* _beforepoll, as modified by poll. (It is therefore not possible
* to have multiple threads simultaneously polling using this
* interface.)
*
* This function actually performs all of the IO and other actions,
* and generates events (libxl_event), which are implied by either
* (a) the time of day or (b) both (i) the returned information from
* _beforepoll, and (ii) the results from poll specified in
* fds[0..nfds-1]. Generated events can then be retrieved by
* libxl_event_check.
*/
void libxl_osevent_afterpoll(libxl_ctx *ctx, int nfds, const struct pollfd *fds,
struct timeval now)
LIBXL_EXTERNAL_CALLERS_ONLY;
typedef struct libxl_osevent_hooks {
int (*fd_register)(void *user, int fd, void **for_app_registration_out,
short events, void *for_libxl);
int (*fd_modify)(void *user, int fd, void **for_app_registration_update,
short events);
void (*fd_deregister)(void *user, int fd, void *for_app_registration);
int (*timeout_register)(void *user, void **for_app_registration_out,
struct timeval abs, void *for_libxl);
int (*timeout_modify)(void *user, void **for_app_registration_update,
struct timeval abs)
/* only ever called with abs={0,0}, meaning ASAP */;
void (*timeout_deregister)(void *user, void *for_app_registration)
/* will never be called */;
} libxl_osevent_hooks;
/* The application which calls register_fd_hooks promises to
* maintain a register of fds and timeouts that libxl is interested
* in, and make calls into libxl (libxl_osevent_occurred_*)
* when those fd events and timeouts occur. This is more efficient
* than _beforepoll/_afterpoll if there are many fds (which can
* happen if the same libxl application is managing many domains).
*
* For an fd event, events is as for poll(). register or modify may
* be called with events==0, in which case it must still work
* normally, just not generate any events.
*
* For a timeout event, milliseconds is as for poll().
* Specifically, negative values of milliseconds mean NO TIMEOUT.
* This is used by libxl to temporarily disable a timeout.
*
* If the register or modify hook succeeds it may update
* *for_app_registration_out/_update and must then return 0.
* On entry to register, *for_app_registration_out is always NULL.
*
* A registration or modification hook may fail, in which case it
* must leave the registration state of the fd or timeout unchanged.
* It may then either return ERROR_OSEVENT_REG_FAIL or any positive
* int. The value returned will be passed up through libxl and
* eventually returned back to the application. When register
* fails, any value stored into *for_registration_out is ignored by
* libxl; when modify fails, any changed value stored into
* *for_registration_update is honoured by libxl and will be passed
* to future modify or deregister calls.
*
* libxl may want to register more than one callback for any one fd;
* in that case: (i) each such registration will have at least one bit
* set in revents which is unique to that registration; (ii) if an
* event occurs which is relevant for multiple registrations the
* application's event system may call libxl_osevent_occurred_fd
* for one, some, or all of those registrations.
*
* If fd_modify is used, it is permitted for the application's event
* system to still make calls to libxl_osevent_occurred_fd for the
* "old" set of requested events; these will be safely ignored by
* libxl.
*
* libxl will remember the value stored in *for_app_registration_out
* (or *for_app_registration_update) by a successful call to
* register (or modify), and pass it to subsequent calls to modify
* or deregister.
*
* Note that the application must cope with a call from libxl to
* timeout_modify racing with its own call to
* libxl__osevent_occurred_timeout. libxl guarantees that
* timeout_modify will only be called with abs={0,0} but the
* application must still ensure that libxl's attempt to cause the
* timeout to occur immediately is safely ignored even the timeout is
* actually already in the process of occurring.
*
* timeout_deregister is not used because it forms part of a
* deprecated unsafe mode of use of the API.
*
* osevent_register_hooks may be called only once for each libxl_ctx.
* libxl may make calls to register/modify/deregister from within
* any libxl function (indeed, it will usually call register from
* register_event_hooks). Conversely, the application MUST NOT make
* the event occurrence calls (libxl_osevent_occurred_*) into libxl
* reentrantly from within libxl (for example, from within the
* register/modify functions).
*
* Lock hierarchy: the register/modify/deregister functions may be
* called with locks held. These locks (the "libxl internal locks")
* are inside the libxl_ctx. Therefore, if those register functions
* acquire any locks of their own ("caller register locks") outside
* libxl, to avoid deadlock one of the following must hold for each
* such caller register lock:
* (a) "acquire libxl internal locks before caller register lock":
* No libxl function may be called with the caller register
* lock held.
* (b) "acquire caller register lock before libxl internal locks":
* No libxl function may be called _without_ the caller
* register lock held.
* Of these we would normally recommend (a).
*
* The value *hooks is not copied and must outlast the libxl_ctx.
*/
void libxl_osevent_register_hooks(libxl_ctx *ctx,
const libxl_osevent_hooks *hooks,
void *user);
/* It is NOT legal to call _occurred_ reentrantly within any libxl
* function. Specifically it is NOT legal to call it from within
* a register callback. Conversely, libxl MAY call register/deregister
* from within libxl_event_occurred_call_*.
*/
void libxl_osevent_occurred_fd(libxl_ctx *ctx, void *for_libxl,
int fd, short events, short revents)
LIBXL_EXTERNAL_CALLERS_ONLY;
/* Implicitly, on entry to this function the timeout has been
* deregistered. If _occurred_timeout is called, libxl will not
* call timeout_deregister; if it wants to requeue the timeout it
* will call timeout_register again.
*/
void libxl_osevent_occurred_timeout(libxl_ctx *ctx, void *for_libxl)
LIBXL_EXTERNAL_CALLERS_ONLY;
/*======================================================================*/
/*
* Subprocess handling.
*
* Unfortunately the POSIX interface makes this very awkward.
*
* There are two possible arrangements for collecting statuses from
* wait/waitpid.
*
* For naive programs:
*
* libxl will keep a SIGCHLD handler installed whenever it has an
* active (unreaped) child. It will reap all children with
* wait(); any children it does not recognise will be passed to
* the application via an optional callback (and will result in
* logged warnings if no callback is provided or the callback
* denies responsibility for the child).
*
* libxl may have children whenever:
*
* - libxl is performing an operation which can be made
* asynchronous; ie one taking a libxl_asyncop_how, even
* if NULL is passed indicating that the operation is
* synchronous; or
*
* - events of any kind are being generated, as requested
* by libxl_evenable_....
*
* A multithreaded application which is naive in this sense may
* block SIGCHLD on some of its threads, but there must be at
* least one thread that has SIGCHLD unblocked. libxl will not
* modify the blocking flag for SIGCHLD (except that it may create
* internal service threads with all signals blocked).
*
* A naive program must only have at any one time only
* one libxl context which might have children.
*
* For programs which run their own children alongside libxl's:
*
* A program which does this must call libxl_childproc_setmode.
* There are three options:
*
* libxl_sigchld_owner_libxl:
*
* While any libxl operation which might use child processes
* is running, works like libxl_sigchld_owner_libxl_always;
* but, deinstalls the handler the rest of the time.
*
* In this mode, the application, while it uses any libxl
* operation which might create or use child processes (see
* above):
* - Must not have any child processes running.
* - Must not install a SIGCHLD handler.
* - Must not reap any children.
*
* This is the default (i.e. if setmode is not called, or 0 is
* passed for hooks).
*
* libxl_sigchld_owner_mainloop:
*
* The application must install a SIGCHLD handler and reap (at
* least) all of libxl's children and pass their exit status to
* libxl by calling libxl_childproc_exited. (If the application
* has multiple libxl ctx's, it must call libxl_childproc_exited
* on each ctx.)
*
* libxl_sigchld_owner_libxl_always:
*
* The application expects this libxl ctx to reap all of the
* process's children, and provides a callback to be notified of
* their exit statuses. The application must have only one
* libxl_ctx configured this way.
*
* libxl_sigchld_owner_libxl_always_selective_reap:
*
* The application expects to reap all of its own children
* synchronously, and does not use SIGCHLD. libxl is to install
* a SIGCHLD handler. The application may have multiple
* libxl_ctxs configured this way; in which case all of its ctxs
* must be so configured.
*/
typedef enum {
/* libxl owns SIGCHLD whenever it has a child, and reaps
* all children, including those not spawned by libxl. */
libxl_sigchld_owner_libxl,
/* Application promises to discover when SIGCHLD occurs and call
* libxl_childproc_exited or libxl_childproc_sigchld_occurred (but
* NOT from within a signal handler). libxl will not itself
* arrange to (un)block or catch SIGCHLD. */
libxl_sigchld_owner_mainloop,
/* libxl owns SIGCHLD all the time, and the application is
* relying on libxl's event loop for reaping its children too. */
libxl_sigchld_owner_libxl_always,
/* libxl owns SIGCHLD all the time, but it must only reap its own
* children. The application will reap its own children
* synchronously with waitpid, without the assistance of SIGCHLD. */
libxl_sigchld_owner_libxl_always_selective_reap,
} libxl_sigchld_owner;
typedef struct {
libxl_sigchld_owner chldowner;
/* All of these are optional: */
/* Called by libxl instead of fork. Should behave exactly like
* fork, including setting errno etc. May NOT reenter into libxl.
* Application may use this to discover pids of libxl's children,
* for example.
*/
pid_t (*fork_replacement)(void *user);
/* With libxl_sigchld_owner_libxl, called by libxl when it has
* reaped a pid. (Not permitted with _owner_mainloop.)
*
* Should return 0 if the child was recognised by the application
* (or if the application does not keep those kind of records),
* ERROR_UNKNOWN_CHILD if the application knows that the child is not
* the application's; if it returns another error code it is a
* disaster as described for libxl_event_register_callbacks.
* (libxl will report unexpected children to its error log.)
*
* If not supplied, the application is assumed not to start
* any children of its own.
*
* This function is NOT called from within the signal handler.
* Rather it will be called from inside a libxl's event handling
* code and thus only when libxl is running, for example from
* within libxl_event_wait. (libxl uses the self-pipe trick
* to implement this.)
*
* childproc_exited_callback may call back into libxl, but it
* is best to avoid making long-running libxl calls as that might
* stall the calling event loop while the nested operation
* completes.
*/
int (*reaped_callback)(pid_t, int status, void *user);
} libxl_childproc_hooks;
/* hooks may be 0 in which is equivalent to &{ libxl_sigchld_owner_libxl, 0, 0 }
*
* May not be called when libxl might have any child processes, or the
* behaviour is undefined. So it is best to call this at
* initialisation.
*/
void libxl_childproc_setmode(libxl_ctx *ctx, const libxl_childproc_hooks *hooks,
void *user);
/*
* This function is for an application which owns SIGCHLD and which
* reaps all of the process's children, and dispatches the exit status
* to the correct place inside the application.
*
* May be called only by an application which has called setmode with
* chldowner == libxl_sigchld_owner_mainloop. If pid was a process started
* by this instance of libxl, returns 0 after doing whatever
* processing is appropriate. Otherwise silently returns
* ERROR_UNKNOWN_CHILD. No other error returns are possible.
*
* May NOT be called from within a signal handler which might
* interrupt any libxl operation. The application will almost
* certainly need to use the self-pipe trick (or a working pselect or
* ppoll) to implement this.
*/
int libxl_childproc_reaped(libxl_ctx *ctx, pid_t, int status)
LIBXL_EXTERNAL_CALLERS_ONLY;
/*
* This function is for an application which owns SIGCHLD but which
* doesn't keep track of all of its own children in a manner suitable
* for reaping all of them and then dispatching them.
*
* Such an the application must notify libxl, by calling this
* function, that a SIGCHLD occurred. libxl will then check all its
* children, reap any that are ready, and take any action necessary -
* but it will not reap anything else.
*
* May be called only by an application which has called setmode with
* chldowner == libxl_sigchld_owner_mainloop.
*
* May NOT be called from within a signal handler which might
* interrupt any libxl operation (just like libxl_childproc_reaped).
*/
void libxl_childproc_sigchld_occurred(libxl_ctx *ctx)
LIBXL_EXTERNAL_CALLERS_ONLY;
/*
* An application which initialises a libxl_ctx in a parent process
* and then forks a child which does not quickly exec, must
* instead libxl_postfork_child_noexec in the child. One call
* on any existing (or specially made) ctx is sufficient; after
* this all previously existing libxl_ctx's are invalidated and
* must not be used - or even freed. It is harmless to call this
* postfork function and then exec anyway.
*
* Until libxl_postfork_child_noexec has returned:
* - No other libxl calls may be made.
* - If any libxl ctx was configured handle the process's SIGCHLD,
* the child may not create further (grand)child processes, nor
* manipulate SIGCHLD.
*
* libxl_postfork_child_noexec may not reclaim all the resources
* associated with the libxl ctx. This includes but is not limited
* to: ordinary memory; files on disk and in /var/run; file
* descriptors; memory mapped into the process from domains being
* managed (grant maps); Xen event channels. Use of libxl in
* processes which fork long-lived children is not recommended for
* this reason. libxl_postfork_child_noexec is provided so that
* an application can make further libxl calls in a child which
* is going to exec or exit soon.
*/
void libxl_postfork_child_noexec(libxl_ctx *ctx);
#endif
/*
* Local variables:
* mode: C
* c-basic-offset: 4
* indent-tabs-mode: nil
* End:
*/
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