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eio_stubs.c
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eio_stubs.c
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#define _GNU_SOURCE
#include <linux/sched.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/eventfd.h>
#if __GLIBC__ > 2 || __GLIBC_MINOR__ > 24
#include <sys/random.h>
#endif
#include <sys/syscall.h>
#include <sys/wait.h>
#include <limits.h>
#include <errno.h>
#include <dirent.h>
#include <fcntl.h>
#include <signal.h>
#include <unistd.h>
// We need caml_convert_signal_number
#define CAML_INTERNALS
#include "primitives.h"
#include <caml/mlvalues.h>
#include <caml/memory.h>
#include <caml/alloc.h>
#include <caml/signals.h>
#include <caml/unixsupport.h>
#include <caml/bigarray.h>
#include "fork_action.h"
#ifndef SYS_pidfd_send_signal
# define SYS_pidfd_send_signal 424
#endif
#ifndef SYS_pidfd_open
# define SYS_pidfd_open 434
#endif
#ifndef SYS_clone3
# define SYS_clone3 435
# define CLONE_PIDFD 0x00001000
#endif
// struct clone_args isn't defined in linux-lts headers, so define it here
// Note that this struct is versioned by size. See linux/sched.h for details
struct caml_eio_clone_args {
uint64_t flags;
uint64_t pidfd;
uint64_t child_tid;
uint64_t parent_tid;
uint64_t exit_signal;
uint64_t stack;
uint64_t stack_size;
uint64_t tls;
};
// Make sure we have enough space for at least one entry.
#define DIRENT_BUF_SIZE (PATH_MAX + sizeof(struct dirent64))
CAMLprim value caml_eio_eventfd(value v_initval) {
int ret;
ret = eventfd(Int_val(v_initval), EFD_CLOEXEC);
if (ret == -1) uerror("eventfd", Nothing);
return Val_int(ret);
}
CAMLprim value caml_eio_mkdirat(value v_fd, value v_path, value v_perm) {
CAMLparam1(v_path);
char *path;
int ret;
caml_unix_check_path(v_path, "mkdirat");
path = caml_stat_strdup(String_val(v_path));
caml_enter_blocking_section();
ret = mkdirat(Int_val(v_fd), path, Int_val(v_perm));
caml_leave_blocking_section();
caml_stat_free(path);
if (ret == -1) uerror("mkdirat", v_path);
CAMLreturn(Val_unit);
}
CAMLprim value caml_eio_renameat(value v_old_fd, value v_old_path, value v_new_fd, value v_new_path) {
CAMLparam2(v_old_path, v_new_path);
char *old_path;
char *new_path;
int ret;
caml_unix_check_path(v_old_path, "renameat-old");
caml_unix_check_path(v_new_path, "renameat-new");
old_path = caml_stat_strdup(String_val(v_old_path));
new_path = caml_stat_strdup(String_val(v_new_path));
caml_enter_blocking_section();
ret = renameat(Int_val(v_old_fd), old_path,
Int_val(v_new_fd), new_path);
caml_leave_blocking_section();
caml_stat_free(old_path);
caml_stat_free(new_path);
if (ret == -1) uerror("renameat", v_old_path);
CAMLreturn(Val_unit);
}
CAMLprim value caml_eio_symlinkat(value v_old_path, value v_new_fd, value v_new_path) {
CAMLparam2(v_old_path, v_new_path);
char *old_path;
char *new_path;
int ret;
caml_unix_check_path(v_old_path, "symlinkat-old");
caml_unix_check_path(v_new_path, "symlinkat-new");
old_path = caml_stat_strdup(String_val(v_old_path));
new_path = caml_stat_strdup(String_val(v_new_path));
caml_enter_blocking_section();
ret = symlinkat(old_path, Int_val(v_new_fd), new_path);
caml_leave_blocking_section();
caml_stat_free(old_path);
caml_stat_free(new_path);
if (ret == -1) uerror("symlinkat", v_old_path);
CAMLreturn(Val_unit);
}
CAMLprim value caml_eio_getrandom(value v_ba, value v_off, value v_len) {
CAMLparam1(v_ba);
ssize_t ret;
ssize_t off = (ssize_t)Long_val(v_off);
ssize_t len = (ssize_t)Long_val(v_len);
do {
void *buf = (char *)Caml_ba_data_val(v_ba) + off;
caml_enter_blocking_section();
#if __GLIBC__ > 2 || __GLIBC_MINOR__ > 24
ret = getrandom(buf, len, 0);
#else
ret = syscall(SYS_getrandom, buf, len, 0);
#endif
caml_leave_blocking_section();
} while (ret == -1 && errno == EINTR);
if (ret == -1) uerror("getrandom", Nothing);
CAMLreturn(Val_long(ret));
}
CAMLprim value caml_eio_getdents(value v_fd) {
CAMLparam1(v_fd);
CAMLlocal2(result, cons);
char buf[DIRENT_BUF_SIZE];
struct dirent64 *d;
int nread, pos;
caml_enter_blocking_section();
nread = syscall(SYS_getdents64, Int_val(v_fd), buf, DIRENT_BUF_SIZE);
caml_leave_blocking_section();
if (nread == -1) uerror("getdents", Nothing);
result = Val_int(0); /* The empty list */
for (pos = 0; pos < nread;) {
d = (struct dirent64 *) (buf + pos);
cons = caml_alloc(2, 0);
Store_field(cons, 0, caml_copy_string_of_os(d->d_name)); // Head
Store_field(cons, 1, result); // Tail
result = cons;
pos += d->d_reclen;
}
CAMLreturn(result);
}
static int pidfd_send_signal(int pidfd, int sig, siginfo_t *info, unsigned int flags) {
return syscall(SYS_pidfd_send_signal, pidfd, sig, info, flags);
}
CAMLprim value caml_eio_pidfd_send_signal(value v_pidfd, value v_signal) {
CAMLparam0();
int res;
res = pidfd_send_signal(Int_val(v_pidfd), caml_convert_signal_number(Int_val(v_signal)), NULL, 0);
if (res == -1) uerror("pidfd_send_signal", Nothing);
CAMLreturn(Val_unit);
}
static int pidfd_open(pid_t pid, unsigned int flags) {
return syscall(SYS_pidfd_open, pid, flags);
}
/* Like clone3, but falls back to fork if not supported.
Also, raises exceptions rather then returning an error. */
static pid_t clone3_with_fallback(struct caml_eio_clone_args *cl_args) {
int *pidfd = (int *)(uintptr_t) cl_args->pidfd;
pid_t child_pid = syscall(SYS_clone3, cl_args, sizeof(struct caml_eio_clone_args));
if (child_pid >= 0)
return child_pid; /* Success! */
if (errno != ENOSYS && errno != EPERM) {
uerror("clone3", Nothing); /* Unknown error */
}
/* Probably Docker's security policy is blocking clone3. Fall back to forking. */
child_pid = fork();
if (child_pid == 0) {
/* We are the child */
return 0;
} else if (child_pid < 0) {
uerror("fork", Nothing);
}
*pidfd = pidfd_open(child_pid, 0); /* Is automatically close-on-exec */
if (*pidfd < 0) {
int e = errno;
kill(child_pid, SIGKILL);
waitpid(child_pid, NULL, 0);
errno = e;
uerror("pidfd_open", Nothing);
}
return child_pid;
}
CAMLprim value caml_eio_clone3(value v_errors, value v_actions) {
CAMLparam1(v_actions);
CAMLlocal1(v_result);
pid_t child_pid;
int pidfd = -1; /* Is automatically close-on-exec */
struct caml_eio_clone_args cl_args = {
.flags = CLONE_PIDFD,
.pidfd = (uintptr_t) &pidfd,
.exit_signal = SIGCHLD, /* Needed for wait4 to work if we exit before exec */
.stack = (uintptr_t) NULL, /* Use copy-on-write parent stack */
.stack_size = 0,
};
child_pid = clone3_with_fallback(&cl_args);
if (child_pid == 0) {
/* Run child actions (doesn't return) */
eio_unix_run_fork_actions(Int_val(v_errors), v_actions);
}
v_result = caml_alloc_tuple(2);
Store_field(v_result, 0, Val_long(child_pid));
Store_field(v_result, 1, Val_int(pidfd));
CAMLreturn(v_result);
}