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Add an implementation using splice() for in-kernel tty copies

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Sadly splice is currently not functional in Linux, so the implementation
is turned off
This commit is contained in:
Kovid Goyal 2022-08-01 19:02:20 +05:30
parent cc7e668ad6
commit e43ca5b031
No known key found for this signature in database
GPG Key ID: 06BC317B515ACE7C
1 changed files with 70 additions and 10 deletions
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60
prewarm-launcher.c
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@ -9,8 +9,18 @@
// for cfmakeraw
#ifdef __APPLE__
#define _DARWIN_C_SOURCE 1
const static int has_splice = 0;
#else
#define _DEFAULT_SOURCE
// for splice()
#define _GNU_SOURCE
#ifdef __linux__
#define HAS_SPLICE
const static int has_splice = 0; // sadly the kernel doesnt support splice between tty fds anymore
// https://www.spinics.net/lists/kernel/msg3799785.html
#else
const static int has_splice = 0;
#endif
#endif
// Includes {{{
@ -597,6 +607,28 @@ send_over_socket(void) {
return true;
}
static void
set_append_mode(int fd, bool yes) {
int val = fcntl(fd, F_GETFL);
if (yes) val |= O_APPEND; else val &= ~O_APPEND;
fcntl(fd, F_SETFL, val);
}
#ifndef HAS_SPLICE
#define splice(...) -1
#endif
static bool
transfer_in_kernel(int from, int to, bool *read_failed) {
if (has_splice) {
ssize_t n = 0;
while ((n = splice(from, NULL, to, NULL, PIPE_BUF, 0)) == -1 && errno == EINTR);
*read_failed = n == 0;
return n > 0;
}
return false;
}
static void
loop(void) {
#define fail(s) { print_error(s, errno); return; }
@ -606,6 +638,8 @@ loop(void) {
#undef init
fd_set readable, writable, errorable;
nfds++;
struct { bool data_available_from_child, data_available_from_self; } sd;
if (has_splice) { set_append_mode(child_master_fd, false); set_append_mode(self_ttyfd, false); }
while (keep_going()) {
if (window_size_dirty) {
@ -615,8 +649,18 @@ loop(void) {
add_window_size_to_buffer();
window_size_dirty = false;
}
const bool can_splice = has_splice && child_master_fd > -1 && self_ttyfd > -1;
static bool splice_ok = true;
if (can_splice && splice_ok) {
wf.self_ttyfd.want_read = !sd.data_available_from_self;
wf.self_ttyfd.want_write = sd.data_available_from_child;
wf.child_master_fd.want_read = !sd.data_available_from_child;
wf.child_master_fd.want_write = sd.data_available_from_self;
if (!splice_ok) { set_append_mode(self_ttyfd, true); set_append_mode(child_master_fd, true); }
} else {
wf.self_ttyfd.want_read = to_child_tty.sz < IO_BUZ_SZ; wf.self_ttyfd.want_write = from_child_tty.sz > 0;
wf.child_master_fd.want_read = from_child_tty.sz < IO_BUZ_SZ; wf.child_master_fd.want_write = to_child_tty.sz > 0;
}
wf.socket_fd.want_write = launch_msg.iov_len > 0 || send_on_socket.sz > 0;
FD_ZERO(&readable); FD_ZERO(&writable); FD_ZERO(&errorable);
@ -626,6 +670,21 @@ loop(void) {
while ((ret = select(nfds, &readable, &writable, &errorable, NULL)) == -1) { if (errno != EINTR) fail("select() failed"); }
if (!ret) continue;
if (can_splice && splice_ok) {
bool read_failed = false;
if (FD_ISSET(self_ttyfd, &readable)) sd.data_available_from_self = true;
if (sd.data_available_from_self && FD_ISSET(child_master_fd, &writable)) {
splice_ok = transfer_in_kernel(self_ttyfd, child_master_fd, &read_failed);
sd.data_available_from_self = false;
if (read_failed) fail("reading in kernel from self tty failed");
}
if (FD_ISSET(child_master_fd, &readable)) sd.data_available_from_child = true;
if (sd.data_available_from_child && FD_ISSET(self_ttyfd, &writable) && splice_ok) {
splice_ok = transfer_in_kernel(child_master_fd, self_ttyfd, &read_failed);
sd.data_available_from_child = false;
if (read_failed) fail("reading in kernel from child tty failed");
}
} else {
if (child_master_fd > -1) {
if (FD_ISSET(child_master_fd, &writable)) if (!from_self_to_child()) fail("writing to child tty failed");
if (FD_ISSET(child_master_fd, &readable)) {
@ -636,6 +695,7 @@ loop(void) {
if (FD_ISSET(self_ttyfd, &readable)) if (!read_from_self_tty()) fail("reading from self tty failed");
if (FD_ISSET(self_ttyfd, &writable)) if (!from_child_to_self()) fail("writing to self tty failed");
}
}
if (signal_read_fd > -1 && FD_ISSET(signal_read_fd, &readable)) if (!read_signals()) fail("reading from signal fd failed");