mtkports/dev-vcs/git/compat/montauk-compat.c

/*
 * montauk-compat.c -- POSIX calls git needs that the Montauk libc does not
 * have. Compiled into libgitcompat.a and placed on the link line ahead of
 * liblibc.a.
 *
 * The rule followed here: a shim either does the real thing, or it fails with
 * an errno git already knows how to report. Nothing pretends to have done
 * work it did not do -- with one deliberate exception, fsync(), noted at its
 * definition.
 */

#include <errno.h>
#include <stddef.h>
#include <stdarg.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <time.h>
#include <unistd.h>
#include <pwd.h>
#include <grp.h>
#include <netdb.h>
#include <poll.h>
#include <signal.h>
#include <termios.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <sys/utsname.h>

/*
 * <montauk.h> is the C mirror of the syscall ABI (the C++ SDK headers under montauk/
 * are C++). Only two calls are used below: SYS_GETUSER for the session user
 * and SYS_TERMSIZE for the terminal geometry.
 */
#include <montauk.h>

/* ==== Identity =======================================================
 *
 * MontaukOS has named users but no numeric uid space: a process runs as
 * whoever is logged into the session. A single fixed non-root id is reported,
 * which makes git's two questions answer correctly -- "am I root?" (no, so it
 * does not relax its safety checks) and "does this repository belong to me?"
 * (yes, since every path reports the same owner).
 */

#define MONTAUK_UID 1000
#define MONTAUK_GID 1000

uid_t getuid(void)  { return MONTAUK_UID; }
uid_t geteuid(void) { return MONTAUK_UID; }
gid_t getgid(void)  { return MONTAUK_GID; }
gid_t getegid(void) { return MONTAUK_GID; }

/* No process tree above us that userspace can see. */
pid_t getppid(void) { return 1; }

int setsid(void) { return getpid(); }

/*
 * Process groups do not exist: every process is its own group, and whatever
 * is reading the terminal is the foreground job. Reporting getpid() from all
 * three keeps progress.c's foreground test (tcgetpgrp(fd) == getpgid(0))
 * true, so the progress meter is drawn instead of suppressed.
 */
pid_t getpgid(pid_t pid) { return pid ? pid : getpid(); }
pid_t getpgrp(void)      { return getpid(); }
pid_t tcgetpgrp(int fd)  { (void) fd; return getpid(); }

int setpgid(pid_t pid, pid_t pgid)
{
	(void) pid; (void) pgid;
	return 0;
}

int gethostname(char *name, size_t len)
{
	static const char host[] = "montauk";

	if (!name || len == 0) {
		errno = EINVAL;
		return -1;
	}
	if (len < sizeof(host)) {
		errno = ENAMETOOLONG;
		return -1;
	}
	memcpy(name, host, sizeof(host));
	return 0;
}

/*
 * No interval timers exist and SIGALRM is never delivered, so nothing is
 * armed and nothing was pending. Only upload-pack's idle timeout calls this,
 * and upload-pack needs sockets to be reachable at all.
 */
unsigned int alarm(unsigned int seconds)
{
	(void) seconds;
	return 0;
}

/* ==== Passwd / group =================================================
 *
 * Answered from the session rather than from a database. git uses this for
 * the fallback author identity and to expand "~"; a wrong-but-plausible entry
 * beats a NULL return, which git reports as "You don't exist. Go away!".
 *
 * getpwnam() only recognises the current user: there is nobody else to look
 * up, and inventing entries for arbitrary names would make "~someone" resolve
 * to a directory that does not exist.
 */

static char pw_name_buf[64];
static char pw_dir_buf[128];

static struct passwd *fill_passwd(void)
{
	static struct passwd pw;
	int len = (int) _mtk_syscall2(MTK_SYS_GETUSER,
	                              (long) pw_name_buf,
	                              (long) sizeof(pw_name_buf));

	if (len <= 0 || pw_name_buf[0] == '\0')
		strcpy(pw_name_buf, "user");
	pw_name_buf[sizeof(pw_name_buf) - 1] = '\0';

	snprintf(pw_dir_buf, sizeof(pw_dir_buf), "0:/users/%s", pw_name_buf);

	pw.pw_name   = pw_name_buf;
	pw.pw_passwd = (char *) "";
	pw.pw_uid    = MONTAUK_UID;
	pw.pw_gid    = MONTAUK_GID;
	pw.pw_gecos  = pw_name_buf;
	pw.pw_dir    = pw_dir_buf;
	pw.pw_shell  = (char *) "";

	return &pw;
}

/*
 * Called first thing from main() (patches/0001-montauk-startup.patch).
 *
 * MontaukOS starts every process with an EMPTY environment -- SYS_SPAWN
 * transfers nothing, so environ is bare no matter who launched git. Without
 * HOME, git silently skips the per-user config: ~/.gitconfig never resolves,
 * so `git config --global user.email ...` has nowhere to write, and the
 * repository config becomes the only place a setting can live. Pointing HOME
 * at the session user's directory is what makes --global work.
 *
 * This is deliberately NOT an __attribute__((constructor)): programs linked
 * with programs/link.ld get no .init_array section (the script does not name
 * one, so the linker drops it), which means constructors silently never run.
 * A call from main() is the only reliable hook.
 *
 * An inherited HOME, should the environment ever start carrying one, wins.
 */
void montauk_startup(void)
{
	if (getenv("HOME"))
		return;
	setenv("HOME", fill_passwd()->pw_dir, 0);
}

struct passwd *getpwuid(uid_t uid)
{
	if (uid != MONTAUK_UID) {
		errno = 0;   /* "no such user", not an error, per POSIX */
		return NULL;
	}
	return fill_passwd();
}

struct passwd *getpwnam(const char *name)
{
	struct passwd *pw = fill_passwd();

	if (!name || strcmp(name, pw->pw_name) != 0) {
		errno = 0;
		return NULL;
	}
	return pw;
}

struct group *getgrnam(const char *name)
{
	(void) name;
	errno = 0;
	return NULL;
}

struct group *getgrgid(gid_t gid)
{
	(void) gid;
	errno = 0;
	return NULL;
}

/* ==== Filesystem =====================================================
 *
 * Symlinks have no representation in the MontaukOS VFS (the ramdisk drops
 * them, ext2 support is read-side only for them), so these fail rather than
 * silently creating something else. git's core.symlinks=false path handles
 * the failure by writing a regular file whose contents are the link target.
 */

int symlink(const char *target, const char *linkpath)
{
	(void) target; (void) linkpath;
	errno = EPERM;
	return -1;
}

ssize_t readlink(const char *path, char *buf, size_t bufsiz)
{
	(void) path; (void) buf; (void) bufsiz;
	errno = EINVAL;   /* "not a symbolic link" -- and nothing here is */
	return -1;
}

int link(const char *oldpath, const char *newpath)
{
	(void) oldpath; (void) newpath;
	errno = EPERM;    /* no hard links; callers fall back to copying */
	return -1;
}

int chown(const char *path, uid_t owner, gid_t group)
{
	(void) path; (void) owner; (void) group;
	errno = EPERM;
	return -1;
}

int lchown(const char *path, uid_t owner, gid_t group)
{
	(void) path; (void) owner; (void) group;
	errno = EPERM;
	return -1;
}

int fchown(int fd, uid_t owner, gid_t group)
{
	(void) fd; (void) owner; (void) group;
	errno = EPERM;
	return -1;
}

/*
 * fsync()/fdatasync() report success without doing anything, which is the one
 * shim here that claims more than it delivers. Failing instead is worse: git
 * treats a failed fsync as a fatal error and aborts the write, so every
 * commit would fail. Data does reach the disk -- the kernel writes through
 * its block cache -- but there is no per-descriptor barrier, so ordering
 * across a power loss is not guaranteed. SYS_FS_SYNC (whole-filesystem
 * flush, used by shutdown) is the closest thing that exists.
 */
int fsync(int fd)
{
	(void) fd;
	return 0;
}

int fdatasync(int fd)
{
	(void) fd;
	return 0;
}

/* ==== Terminal input =================================================
 *
 * MontaukOS has no /dev/tty, so compat/terminal.c compiles its fallback
 * branch, and every interactive prompt git makes -- passphrases included --
 * arrives here.
 *
 * THE INPUT IS ECHOED. The libc reads stdin through SYS_GETCHAR and echoes
 * each character itself; there is no line discipline to turn that off (see
 * tcsetattr below, which is why it cannot help). Nothing in this port prompts
 * for a secret today, since there are no network transports and no credential
 * helper, but anything added later must not assume this hides what is typed.
 */
char *getpass(const char *prompt)
{
	static char buf[256];
	size_t len;

	if (prompt && *prompt) {
		fputs(prompt, stderr);
		fflush(stderr);
	}

	if (!fgets(buf, sizeof(buf), stdin))
		return NULL;

	len = strlen(buf);
	while (len > 0 && (buf[len - 1] == '\n' || buf[len - 1] == '\r'))
		buf[--len] = '\0';

	return buf;
}

/* ==== exec ===========================================================
 *
 * execl()/execlp() collect their variadic arguments into an argv and defer to
 * the libc's execv()/execvp(). Those fail with ENOSYS -- MontaukOS spawns new
 * processes (SYS_SPAWN) rather than replacing the current image -- so these
 * fail too, which is what the one caller (`git help`, launching a man viewer)
 * is prepared for.
 *
 * MAX_EXEC_ARGV is generous for that caller; a longer list is rejected
 * outright rather than silently truncated into a different command.
 */

#define MAX_EXEC_ARGV 64

static int collect_exec_argv(const char *arg, va_list ap,
                             const char *argv[], int max)
{
	int argc = 0;

	argv[argc++] = arg;
	while (argc < max) {
		const char *next = va_arg(ap, const char *);

		argv[argc++] = next;
		if (!next)
			return argc;
	}
	return -1;
}

int execl(const char *path, const char *arg, ...)
{
	const char *argv[MAX_EXEC_ARGV];
	va_list ap;
	int argc;

	va_start(ap, arg);
	argc = collect_exec_argv(arg, ap, argv, MAX_EXEC_ARGV);
	va_end(ap);

	if (argc < 0) {
		errno = E2BIG;
		return -1;
	}
	return execv(path, (char *const *) argv);
}

int execlp(const char *file, const char *arg, ...)
{
	const char *argv[MAX_EXEC_ARGV];
	va_list ap;
	int argc;

	va_start(ap, arg);
	argc = collect_exec_argv(arg, ap, argv, MAX_EXEC_ARGV);
	va_end(ap);

	if (argc < 0) {
		errno = E2BIG;
		return -1;
	}
	return execvp(file, (char *const *) argv);
}

/* ==== Signals ========================================================
 *
 * sigaction() over signal(). MontaukOS delivers SIGINT and nothing else, and
 * has no per-process signal mask, so sa_mask and sa_flags (including
 * SA_RESTART) are accepted and ignored -- there are no restartable syscalls
 * to interrupt. The sigset_t operations maintain a bitmask that nothing
 * reads; they exist so callers that build a mask before installing a handler
 * compile and behave predictably.
 */

int sigemptyset(sigset_t *set)
{
	if (set)
		*set = 0;
	return 0;
}

int sigfillset(sigset_t *set)
{
	if (set)
		*set = ~(sigset_t)0;
	return 0;
}

int sigaddset(sigset_t *set, int signum)
{
	if (!set || signum <= 0 || signum >= (int)(8 * sizeof(sigset_t))) {
		errno = EINVAL;
		return -1;
	}
	*set |= (sigset_t)1 << signum;
	return 0;
}

int sigdelset(sigset_t *set, int signum)
{
	if (!set || signum <= 0 || signum >= (int)(8 * sizeof(sigset_t))) {
		errno = EINVAL;
		return -1;
	}
	*set &= ~((sigset_t)1 << signum);
	return 0;
}

int sigismember(const sigset_t *set, int signum)
{
	if (!set || signum <= 0 || signum >= (int)(8 * sizeof(sigset_t))) {
		errno = EINVAL;
		return -1;
	}
	return (*set & ((sigset_t)1 << signum)) != 0;
}

int sigaction(int signum, const struct sigaction *act, struct sigaction *old)
{
	sighandler_t prev;

	if (act) {
		prev = signal(signum, act->sa_handler);
	} else {
		/* Query only: read the handler back by reinstalling it. */
		prev = signal(signum, SIG_DFL);
		if (prev != SIG_ERR)
			signal(signum, prev);
	}

	if (prev == SIG_ERR)
		return -1;

	if (old) {
		memset(old, 0, sizeof(*old));
		old->sa_handler = prev;
	}
	return 0;
}

/* No signal mask exists to block anything with; report an empty one. */
int sigprocmask(int how, const sigset_t *set, sigset_t *old)
{
	(void) how; (void) set;
	if (old)
		*old = 0;
	return 0;
}

/* ==== Time ===========================================================
 *
 * The libc's localtime()/gmtime() use a static buffer; copy it out. Safe
 * here because the port is built NO_PTHREADS.
 */

struct tm *localtime_r(const time_t *timep, struct tm *result)
{
	struct tm *tmp = localtime(timep);

	if (!tmp || !result)
		return NULL;
	*result = *tmp;
	return result;
}

struct tm *gmtime_r(const time_t *timep, struct tm *result)
{
	struct tm *tmp = gmtime(timep);

	if (!tmp || !result)
		return NULL;
	*result = *tmp;
	return result;
}

char *ctime_r(const time_t *timep, char *buf)
{
	char *s = ctime(timep);

	if (!s || !buf)
		return NULL;
	strcpy(buf, s);   /* caller supplies the POSIX-required 26 bytes */
	return buf;
}

char *asctime_r(const struct tm *tm, char *buf)
{
	char *s = asctime(tm);

	if (!s || !buf)
		return NULL;
	strcpy(buf, s);
	return buf;
}

/* ==== Terminal =======================================================
 *
 * There is no line discipline to query or configure: the libc reads stdin a
 * character at a time through SYS_GETCHAR and echoes it itself. tcgetattr
 * hands back a zeroed struct and tcsetattr accepts whatever it is given,
 * because git treats a tcgetattr failure as "this is not a terminal" -- which
 * would disable interactive prompting altogether -- and dies on some
 * tcsetattr failures.
 *
 * The practical consequence: echo cannot be turned off, so a passphrase typed
 * at a git prompt is visible. Nothing in this port prompts for one today
 * (there are no network transports and no credential helper).
 */

int tcgetattr(int fd, struct termios *t)
{
	if (!isatty(fd)) {
		errno = ENOTTY;
		return -1;
	}
	if (t)
		memset(t, 0, sizeof(*t));
	return 0;
}

int tcsetattr(int fd, int actions, const struct termios *t)
{
	(void) actions; (void) t;
	if (!isatty(fd)) {
		errno = ENOTTY;
		return -1;
	}
	return 0;
}

/*
 * The only ioctl git issues is TIOCGWINSZ, and MontaukOS answers that one
 * directly through SYS_TERMSIZE, so the progress meter and `git column` get
 * the real terminal width instead of the 80-column fallback. Every other
 * request fails.
 */
int ioctl(int fd, unsigned long request, ...)
{
	(void) fd;

	if (request == TIOCGWINSZ) {
		va_list ap;
		struct winsize *ws;
		int cols = 0, rows = 0;

		va_start(ap, request);
		ws = va_arg(ap, struct winsize *);
		va_end(ap);

		if (!ws) {
			errno = EFAULT;
			return -1;
		}

		mtk_termsize(&cols, &rows);
		if (cols <= 0 || rows <= 0) {
			errno = ENOTTY;
			return -1;
		}

		ws->ws_col = (unsigned short) cols;
		ws->ws_row = (unsigned short) rows;
		ws->ws_xpixel = 0;
		ws->ws_ypixel = 0;
		return 0;
	}

	errno = ENOTTY;
	return -1;
}

/* ==== poll ===========================================================
 *
 * Only ever called on the pipe ends of a spawned sub-process, and MontaukOS
 * has neither pipe() nor fork(), so this is unreachable in practice. It
 * reports every descriptor ready rather than failing, so that a caller which
 * does get here proceeds to the read() that reports the real error instead of
 * spinning.
 */
int poll(struct pollfd *fds, nfds_t nfds, int timeout)
{
	nfds_t i;

	(void) timeout;

	if (!fds)
		return 0;

	for (i = 0; i < nfds; i++)
		fds[i].revents = fds[i].events;

	return (int) nfds;
}

/* ==== Sockets ========================================================
 *
 * MontaukOS TCP lives behind IPC handles (montauk::socket), not file
 * descriptors, and git hands transport descriptors to sub-processes. Until
 * something bridges the two, every call fails with ENOSYS; `git clone
 * git://...` reports that it cannot connect. Local paths are unaffected.
 */

#define SOCKET_STUB_BODY  do { errno = ENOSYS; return -1; } while (0)

int socket(int domain, int type, int protocol)
{
	(void) domain; (void) type; (void) protocol;
	SOCKET_STUB_BODY;
}

int connect(int fd, const struct sockaddr *addr, socklen_t len)
{
	(void) fd; (void) addr; (void) len;
	SOCKET_STUB_BODY;
}

int bind(int fd, const struct sockaddr *addr, socklen_t len)
{
	(void) fd; (void) addr; (void) len;
	SOCKET_STUB_BODY;
}

int listen(int fd, int backlog)
{
	(void) fd; (void) backlog;
	SOCKET_STUB_BODY;
}

int accept(int fd, struct sockaddr *addr, socklen_t *len)
{
	(void) fd; (void) addr; (void) len;
	SOCKET_STUB_BODY;
}

int shutdown(int fd, int how)
{
	(void) fd; (void) how;
	SOCKET_STUB_BODY;
}

int setsockopt(int fd, int level, int name, const void *val, socklen_t len)
{
	(void) fd; (void) level; (void) name; (void) val; (void) len;
	SOCKET_STUB_BODY;
}

int getsockopt(int fd, int level, int name, void *val, socklen_t *len)
{
	(void) fd; (void) level; (void) name; (void) val; (void) len;
	SOCKET_STUB_BODY;
}

int getsockname(int fd, struct sockaddr *addr, socklen_t *len)
{
	(void) fd; (void) addr; (void) len;
	SOCKET_STUB_BODY;
}

int getpeername(int fd, struct sockaddr *addr, socklen_t *len)
{
	(void) fd; (void) addr; (void) len;
	SOCKET_STUB_BODY;
}

ssize_t send(int fd, const void *buf, size_t len, int flags)
{
	(void) fd; (void) buf; (void) len; (void) flags;
	errno = ENOSYS;
	return -1;
}

ssize_t recv(int fd, void *buf, size_t len, int flags)
{
	(void) fd; (void) buf; (void) len; (void) flags;
	errno = ENOSYS;
	return -1;
}

/* ==== Name resolution ================================================
 *
 * DNS is resolved inside the kernel network stack; no resolver interface is
 * exposed to userspace. Lookups therefore fail, which git reports as an
 * unresolvable host.
 */

int h_errno;

struct hostent *gethostbyname(const char *name)
{
	(void) name;
	h_errno = HOST_NOT_FOUND;
	return NULL;
}

struct servent *getservbyname(const char *name, const char *proto)
{
	(void) name; (void) proto;
	return NULL;
}

int getaddrinfo(const char *node, const char *service,
                const struct addrinfo *hints, struct addrinfo **res)
{
	(void) node; (void) service; (void) hints;
	if (res)
		*res = NULL;
	return EAI_FAIL;
}

void freeaddrinfo(struct addrinfo *res)
{
	(void) res;
}

int getnameinfo(const struct sockaddr *sa, socklen_t salen,
                char *host, socklen_t hostlen,
                char *serv, socklen_t servlen, int flags)
{
	(void) sa; (void) salen; (void) host; (void) hostlen;
	(void) serv; (void) servlen; (void) flags;
	return EAI_FAIL;
}

const char *gai_strerror(int errcode)
{
	(void) errcode;
	return "name resolution is not available on MontaukOS";
}

in_addr_t inet_addr(const char *cp)
{
	(void) cp;
	return INADDR_NONE;
}

char *inet_ntoa(struct in_addr in)
{
	static char buf[16];
	unsigned int a = (unsigned int) in.s_addr;

	snprintf(buf, sizeof(buf), "%u.%u.%u.%u",
	         a & 0xff, (a >> 8) & 0xff, (a >> 16) & 0xff, (a >> 24) & 0xff);
	return buf;
}

/* ==== uname ==========================================================
 *
 * Static answers: there is no kernel interface for the release/version
 * strings. Feeds `git version --build-options` and `git bugreport`.
 */
int uname(struct utsname *buf)
{
	if (!buf) {
		errno = EFAULT;
		return -1;
	}
	memset(buf, 0, sizeof(*buf));
	strcpy(buf->sysname, "MontaukOS");
	strcpy(buf->nodename, "montauk");
	strcpy(buf->release, "");
	strcpy(buf->version, "");
	strcpy(buf->machine, "x86_64");
	return 0;
}