This adds a new system call, epoll_mod_wait. It's described as below:
NAME
epoll_mod_wait - modify and wait for I/O events on an epoll file
descriptor
SYNOPSIS
int epoll_mod_wait(int epfd, int flags,
int ncmds, struct epoll_mod_cmd *cmds,
struct epoll_wait_spec *spec);
DESCRIPTION
The epoll_mod_wait() system call can be seen as an enhanced combination
of several epoll_ctl(2) calls, which are followed by an epoll_pwait(2)
call. It is superior in two cases:
1) When epoll_ctl(2) are followed by epoll_wait(2), using epoll_mod_wait
will save context switches between user mode and kernel mode;
2) When you need higher precision than microsecond for wait timeout.
The epoll_ctl(2) operations are embedded into this call by with ncmds
and cmds. The latter is an array of command structs:
struct epoll_mod_cmd {
/* Reserved flags for future extension, must be 0 for now. */
int flags;
/* The same as epoll_ctl() op parameter. */
int op;
/* The same as epoll_ctl() fd parameter. */
int fd;
/* The same as the "events" field in struct epoll_event. */
uint32_t events;
/* The same as the "data" field in struct epoll_event. */
uint64_t data;
/* Output field, will be set to the return code once this
* command is executed by kernel */
int error;
};
There is no guartantee that all the commands are executed in order. Only
if all the commands are successfully executed (all the error fields are
set to 0), events are polled.
The last parameter "spec" is a pointer to struct epoll_wait_spec, which
contains the information about how to poll the events. If it's NULL, this
call will immediately return after running all the commands in cmds.
The structure is defined as below:
struct epoll_wait_spec {
/* The same as "maxevents" in epoll_pwait() */
int maxevents;
/* The same as "events" in epoll_pwait() */
struct epoll_event *events;
/* Which clock to use for timeout */
int clockid;
/* Maximum time to wait if there is no event */
struct timespec timeout;
/* The same as "sigmask" in epoll_pwait() */
sigset_t *sigmask;
/* The same as "sigsetsize" in epoll_pwait() */
size_t sigsetsize;
} EPOLL_PACKED;
RETURN VALUE
When any error occurs, epoll_mod_wait() returns -1 and errno is set
appropriately. All the "error" fields in cmds are unchanged before they
are executed, and if any cmds are executed, the "error" fields are set
to a return code accordingly. See also epoll_ctl for more details of the
return code.
When successful, epoll_mod_wait() returns the number of file
descriptors ready for the requested I/O, or zero if no file descriptor
became ready during the requested timeout milliseconds.
If spec is NULL, it returns 0 if all the commands are successful, and -1
if an error occured.
ERRORS
These errors apply on either the return value of epoll_mod_wait or error
status for each command, respectively.
EBADF epfd or fd is not a valid file descriptor.
EFAULT The memory area pointed to by events is not accessible with write
permissions.
EINTR The call was interrupted by a signal handler before either any of
the requested events occurred or the timeout expired; see
signal(7).
EINVAL epfd is not an epoll file descriptor, or maxevents is less than
or equal to zero, or fd is the same as epfd, or the requested
operation op is not supported by this interface.
EEXIST op was EPOLL_CTL_ADD, and the supplied file descriptor fd is
already registered with this epoll instance.
ENOENT op was EPOLL_CTL_MOD or EPOLL_CTL_DEL, and fd is not registered
with this epoll instance.
ENOMEM There was insufficient memory to handle the requested op control
operation.
ENOSPC The limit imposed by /proc/sys/fs/epoll/max_user_watches was
encountered while trying to register (EPOLL_CTL_ADD) a new file
descriptor on an epoll instance. See epoll(7) for further
details.
EPERM The target file fd does not support epoll.
CONFORMING TO
epoll_mod_wait() is Linux-specific.
SEE ALSO
epoll_create(2), epoll_ctl(2), epoll_wait(2), epoll_pwait(2), epoll(7)
Fam Zheng (6):
epoll: Extract epoll_wait_do and epoll_pwait_do
epoll: Specify clockid explicitly
epoll: Add definition for epoll_mod_wait structures
epoll: Extract ep_ctl_do
epoll: Add implementation for epoll_mod_wait
x86: Hook up epoll_mod_wait syscall
arch/x86/syscalls/syscall_32.tbl | 1 +
arch/x86/syscalls/syscall_64.tbl | 1 +
fs/eventpoll.c | 219 +++++++++++++++++++++++++--------------
include/linux/syscalls.h | 5 +
include/uapi/linux/eventpoll.h | 20 ++++
5 files changed, 167 insertions(+), 79 deletions(-)
--
1.9.3
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