We can get both in the same system call, so we might as well, rather than having two different functions that make the system call twice. --- When we introduce vsockserverd, it will have to be able to figure out both of these values for the socket it is given to be able to set VSOCKLOCALCID and VSOCKLOCALPORT. vsock.c | 9 ++++++--- vsock.h | 5 +++-- vsockserver.c | 2 +- 3 files changed, 10 insertions(+), 6 deletions(-) diff --git a/vsock.c b/vsock.c index e6a173c..99945c3 100644 --- a/vsock.c +++ b/vsock.c @@ -1,5 +1,5 @@ // SPDX-License-Identifier: GPL-2.0-or-later -// SPDX-FileCopyrightText: 2020 Alyssa Ross +// SPDX-FileCopyrightText: 2020-2021 Alyssa Ross #define _GNU_SOURCE @@ -62,7 +62,7 @@ int vsock_open(uint32_t cid, uint32_t port) return fd; } -int vsock_get_port(int fd, uint32_t *port) +int vsock_get_cid_and_port(int fd, uint32_t *cid, uint32_t *port) { struct sockaddr_vm addr; socklen_t addrlen = sizeof addr; @@ -70,7 +70,10 @@ int vsock_get_port(int fd, uint32_t *port) if (getsockname(fd, (struct sockaddr *)&addr, &addrlen) == -1) return -1; - *port = addr.svm_port; + if (cid) + *cid = addr.svm_cid; + if (port) + *port = addr.svm_port; return 0; } diff --git a/vsock.h b/vsock.h index e7d66c9..e7ffd62 100644 --- a/vsock.h +++ b/vsock.h @@ -1,5 +1,5 @@ // SPDX-License-Identifier: GPL-2.0-or-later -// SPDX-FileCopyrightText: 2020 Alyssa Ross +// SPDX-FileCopyrightText: 2020-2021 Alyssa Ross #include @@ -9,4 +9,5 @@ int vsock_accept(int sockfd, uint32_t *cid, uint32_t *port); int vsock_connect(int fd, uint32_t cid, uint32_t port); int vsock_open(uint32_t cid, uint32_t port); -int vsock_get_port(int fd, uint32_t *port); +// `cid' and `port' can be null. +int vsock_get_cid_and_port(int fd, uint32_t *cid, uint32_t *port); diff --git a/vsockserver.c b/vsockserver.c index df9d334..58cd063 100644 --- a/vsockserver.c +++ b/vsockserver.c @@ -80,7 +80,7 @@ int main(int argc, char *argv[]) diee(EX_OSERR, "listen"); if (lport == VMADDR_PORT_ANY) - if (vsock_get_port(fd, &lport) == -1) + if (vsock_get_cid_and_port(fd, NULL, &lport) == -1) diee(EX_OSERR, "getsockname"); if (notify) { -- 2.30.0

This is entirely an implementation detail, for the moment, but it becomes important when we split out vsockserver into two seperate programs, one for binding the socket, and one for accepting, like s6-networking. Non-blocking sockets are the default there, so it makes sense to share that behaviour. I added the comment about blockingness of the connection sockets just in case, but for now Linux is the only Unix with an AF_VSOCK implementation, so I don't expect it to become relevant any time soon. --- vsockserver.c | 20 +++++++++++++++++--- 1 file changed, 17 insertions(+), 3 deletions(-) diff --git a/vsockserver.c b/vsockserver.c index 58cd063..43307d2 100644 --- a/vsockserver.c +++ b/vsockserver.c @@ -4,7 +4,9 @@ #define _GNU_SOURCE #include +#include #include +#include #include #include #include @@ -33,7 +35,7 @@ noreturn static void ex_usage(void) int main(int argc, char *argv[]) { bool notify = false; - int opt, conn; + int opt; pid_t child; uint32_t lcid, lport, rcid, rport; @@ -73,6 +75,9 @@ int main(int argc, char *argv[]) if (fd == -1) diee(EX_OSERR, "socket"); + if (fcntl(fd, F_SETFL, O_NONBLOCK) == -1) + diee(EX_OSERR, "fcntl"); + if (vsock_bind(fd, lcid, lport) == -1) diee(EX_OSERR, "bind"); @@ -93,7 +98,16 @@ int main(int argc, char *argv[]) ilog("listening as %" PRIu32 " on port %" PRIu32, lcid, lport); - while ((conn = vsock_accept(fd, &rcid, &rport)) != -1) { + struct pollfd poll_fd = { .fd = fd, .events = POLL_IN, .revents = 0 }; + while (poll(&poll_fd, 1, -1) != -1) { + // On Linux, conn will be blocking. On other + // platforms, this may not be the case. If other + // platforms are to be supported, we'd probably want + // to set O_NONBLOCK here. + int conn = vsock_accept(fd, &rcid, &rport); + if (conn == -1) + diee(EX_OSERR, "accept"); + setenvf("VSOCKREMOTECID", 1, "%" PRIu32, rcid); setenvf("VSOCKREMOTEPORT", 1, "%" PRIu32, rport); @@ -117,5 +131,5 @@ int main(int argc, char *argv[]) close(conn); } - diee(EX_OSERR, "accept"); + diee(EX_OSERR, "poll"); } -- 2.30.0

This is useful if we want to provide a more specific error message than strerror can provide. --- log.c | 10 ++++++++++ log.h | 8 ++++---- 2 files changed, 14 insertions(+), 4 deletions(-) diff --git a/log.c b/log.c index cdfacd6..8a57105 100644 --- a/log.c +++ b/log.c @@ -62,6 +62,16 @@ void ilog(const char *fmt, ...) va_end(ap); } +void die(int eval, const char *fmt, ...) +{ + va_list ap; + va_start(ap, fmt); + velog(fmt, ap); + va_end(ap); + + exit(eval); +} + void diee(int eval, const char *fmt, ...) { va_list ap; diff --git a/log.h b/log.h index 7b40e48..706d42f 100644 --- a/log.h +++ b/log.h @@ -11,20 +11,20 @@ enum verbosity { extern enum verbosity verbosity; +// Functions with an `e' suffix additionally print strerrno(errno). + // If opt is a character that matches a standard UCSPI command line // verbosity option, sets the verbosity appropriately and returns // true. Otherwise, returns false. _Bool set_verbosity(int opt); -// Log an error message, followed by strerrno(errno), then exit with -// status eval. +// Log an error message then exit with status eval. +_Noreturn void die(int eval, const char *fmt, ...); _Noreturn void diee(int eval, const char *fmt, ...); // Log an error message. void elog(const char *fmt, ...); void velog(const char *fmt, va_list args); - -// Log an error message, followed by strerror(errno). void veloge(const char *fmt, va_list args); // Log an informative message. -- 2.30.0

vsockserver-socketbinder creates and listens on a socket, and vsockserverd accepts connections and sets up file descriptors. vsockserver previously did both of these things in one big program, but now it just sets up a command line to run vsockserver-socketbinder followed by vsockserverd. Having two seperate programs allows one program to be used in situations where the other is not suitable (e.g. using vsockserver-socketbinder to create a socket in situations where accept behaviour more complex than vsockserverd can provide is required). This design is taken from s6[1], which uses the same design for its s6-ipcserver, s6-ipcserver-socketbinder, and s6-ipcserverd programs. [1]: https://skarnet.org/software/s6/ --- Because vsockserver.c is completely rewritten in this patch, the diff generated by git was a bit confusing, so the diff here has been lovingly hand-edited to group the hunks together more and make it easy to see the new code all at once. Being able to do this is one of the nice things about email patches. ;) The new implementations are much more thoroughly commented. Think that's my new style. :) .gitignore | 2 + Makefile.in | 14 ++- vsockserver-socketbinder.c | 86 ++++++++++++++++++ vsockserver.c | 149 ++++++++++++++------------------ vsockserver.c => vsockserverd.c | 65 ++++++-------- 5 files changed, 186 insertions(+), 130 deletions(-) create mode 100644 vsockserver-socketbinder.c copy vsockserver.c => vsockserverd.c (64%) diff --git a/.gitignore b/.gitignore index 89a0408..d29518a 100644 --- a/.gitignore +++ b/.gitignore @@ -4,6 +4,8 @@ *.o *.tmp vsockclient +vsockserver-socketbinder +vsockserverd vsockserver config.h Makefile diff --git a/Makefile.in b/Makefile.in index 3260e85..0e65f1f 100644 --- a/Makefile.in +++ b/Makefile.in @@ -10,7 +10,7 @@ INSTALL_PROGRAM = $(INSTALL) prefix = @PREFIX@ bindir = @BINDIR@ -PROGRAMS = vsockclient vsockserver +PROGRAMS = vsockclient vsockserver-socketbinder vsockserverd vsockserver all: $(PROGRAMS) .PHONY: all @@ -26,11 +26,17 @@ config.h: configure vsockclient: vsockclient.o env.o log.o num.o vsock.o $(CC) $(LDFLAGS) -o $@ $@.o env.o log.o num.o vsock.o $(LDLIBS) -vsockserver: vsockserver.o env.o log.o num.o vsock.o - $(CC) $(LDFLAGS) -o $@ $@.o env.o log.o num.o vsock.o $(LDLIBS) +vsockserver-socketbinder: vsockserver-socketbinder.o log.o num.o vsock.o + $(CC) $(LDFLAGS) -o $@ $@.o log.o num.o vsock.o $(LDLIBS) +vsockserverd: vsockserverd.o env.o log.o vsock.o + $(CC) $(LDFLAGS) -o $@ $@.o env.o log.o vsock.o $(LDLIBS) +vsockserver: vsockserver.o exec.o log.o + $(CC) $(LDFLAGS) -o $@ $@.o exec.o log.o $(LDLIBS) vsockclient.o: env.h log.h num.h vsock.h -vsockserver.o: env.h log.h num.h vsock.h +vsockserver-socketbinder.o: log.h num.h vsock.h +vsockserverd.o: env.h log.h vsock.h +vsockserver.o: config.h exec.h log.h clean: rm -f $(PROGRAMS) *.o diff --git a/vsockserver-socketbinder.c b/vsockserver-socketbinder.c new file mode 100644 index 0000000..598c01c --- /dev/null +++ b/vsockserver-socketbinder.c @@ -0,0 +1,86 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +// SPDX-FileCopyrightText: 2020-2021 Alyssa Ross + +#define _GNU_SOURCE + +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#include + +#include "log.h" +#include "num.h" +#include "vsock.h" + +noreturn static void ex_usage(void) +{ + if (verbosity) + fprintf(stderr, "Usage: %s cid port prog...\n", + program_invocation_short_name); + exit(EX_USAGE); +} + +int main(int argc, char *argv[]) +{ + int opt, fd; + uint32_t cid, port; + + // A skeleton of an option parser to reject any options that + // are given, so we can add options in the future without + // worrying about breaking backwards compatibility because + // they were previously interpreted as a first argument. + while ((opt = getopt(argc, argv, "+")) != -1) { + switch (opt) { + default: + ex_usage(); + } + } + + // Check there are enough positional arguments (two for the + // address and at least one to exec into). + if (optind > argc - 3) + ex_usage(); + + // Parse the `cid' argument. + if (!strcmp(argv[optind], "-1")) + cid = VMADDR_CID_ANY; + else if (getu32(argv[optind], 0, UINT32_MAX, &cid)) + ex_usage(); + optind++; + + // Parse the `port' argument. + if (!strcmp(argv[optind], "-1")) + port = VMADDR_PORT_ANY; + else if (getu32(argv[optind], 0, UINT32_MAX, &port)) + ex_usage(); + optind++; + + // Set up the socket. + fd = socket(AF_VSOCK, SOCK_STREAM, 0); + if (fd == -1) + diee(EX_OSERR, "socket"); + if (fcntl(fd, F_SETFL, O_NONBLOCK) == -1) + diee(EX_OSERR, "fcntl"); + if (vsock_bind(fd, cid, port) == -1) + diee(EX_OSERR, "bind"); + if (listen(fd ,40) == -1) + diee(EX_OSERR, "listen"); + + // Place the socket at stdout. + if (dup2(fd, STDIN_FILENO) == -1) + diee(EX_OSERR, "dup2"); + if (fd != STDIN_FILENO) + close(fd); + + // Finally, exec into `prog'. + execvp(argv[optind], &argv[optind]); + diee(EX_OSERR, "execvp"); +} diff --git a/vsockserver.c b/vsockserver.c index 43307d2..f740a8a 100644 --- a/vsockserver.c +++ b/vsockserver.c @@ -1,28 +1,20 @@ // SPDX-License-Identifier: GPL-2.0-or-later -// SPDX-FileCopyrightText: 2020-2021 Alyssa Ross +// SPDX-FileCopyrightText: 2021 Alyssa Ross #define _GNU_SOURCE +#include #include -#include -#include -#include #include #include #include #include -#include -#include -#include #include #include -#include - -#include "env.h" +#include "config.h" +#include "exec.h" #include "log.h" -#include "num.h" -#include "vsock.h" noreturn static void ex_usage(void) { @@ -34,102 +26,87 @@ noreturn static void ex_usage(void) int main(int argc, char *argv[]) { - bool notify = false; int opt; - pid_t child; - uint32_t lcid, lport, rcid, rport; + bool alloc_failed = false; + size_t binder_opts_len = 0, daemon_opts_len = 0; + char *binder_opts = NULL, *daemon_opts = NULL; + + // The heavy lifting here is done by vsockserver-socketbinder + // and vsockserverd. All this program does is munge argv + // appropriately to set the right options for each of those + // programs, and then exec into vsockserver-socketbinder. + + // If allocation fails, we need to keep going until after + // we've parsed the arguments, so we know what our verbosity + // setting is, and consequently whether we should print an + // error message about the allocation failure. + alloc_failed |= + argz_add(&binder_opts, &binder_opts_len, BINDIR "/vsockserver-socketbinder") || + argz_add(&daemon_opts, &daemon_opts_len, BINDIR "/vsockserverd"); while ((opt = getopt(argc, argv, "+1qQv")) != -1) { + char *arg = NULL; + switch (opt) { case '1': - notify = true; - break; case 'q': case 'Q': case 'v': set_verbosity(opt); + alloc_failed |= + asprintf(&arg, "-%c", opt) == -1 || + argz_add(&daemon_opts, &daemon_opts_len, arg); + free(arg); break; default: ex_usage(); } } + // Now that verbosity is set, we can whether we were sitting + // on an allocation failure. + if (alloc_failed) + diee(EX_OSERR, "malloc"); + // Now we don't have to keep checking alloc_failed before + // doing anything, and we can deal with allocation failures + // after this point by just terminating immediately. + - // Check there are enough positional arguments (two for the - // address and at least one to exec into). + // Check there are `cid' and `port' arguments to pass to + // vsockserver-socketbinder, and at least one `prog' argument + // to pass to vsockserverd. if (optind > argc - 3) ex_usage(); - if (!strcmp(argv[optind], "-1")) - lcid = VMADDR_CID_ANY; - else if (getu32(argv[optind], 0, UINT32_MAX, &lcid)) - ex_usage(); - optind++; - - if (!strcmp(argv[optind], "-1")) - lport = VMADDR_PORT_ANY; - else if (getu32(argv[optind], 0, UINT32_MAX, &lport)) - ex_usage(); - optind++; - - int fd = socket(AF_VSOCK, SOCK_STREAM, 0); - if (fd == -1) - diee(EX_OSERR, "socket"); - - if (fcntl(fd, F_SETFL, O_NONBLOCK) == -1) - diee(EX_OSERR, "fcntl"); - - if (vsock_bind(fd, lcid, lport) == -1) - diee(EX_OSERR, "bind"); - - if (listen(fd, 40) == -1) - diee(EX_OSERR, "listen"); - - if (lport == VMADDR_PORT_ANY) - if (vsock_get_cid_and_port(fd, NULL, &lport) == -1) - diee(EX_OSERR, "getsockname"); - - if (notify) { - printf("%" PRIu32 "\n", lport); - fclose(stdout); - } - - setenvf("VSOCKLOCALCID", 1, "%" PRIu32, lcid); - setenvf("VSOCKLOCALPORT", 1, "%" PRIu32, lport); - - ilog("listening as %" PRIu32 " on port %" PRIu32, lcid, lport); - - struct pollfd poll_fd = { .fd = fd, .events = POLL_IN, .revents = 0 }; - while (poll(&poll_fd, 1, -1) != -1) { - // On Linux, conn will be blocking. On other - // platforms, this may not be the case. If other - // platforms are to be supported, we'd probably want - // to set O_NONBLOCK here. - int conn = vsock_accept(fd, &rcid, &rport); - if (conn == -1) - diee(EX_OSERR, "accept"); - - setenvf("VSOCKREMOTECID", 1, "%" PRIu32, rcid); - setenvf("VSOCKREMOTEPORT", 1, "%" PRIu32, rport); - - ilog("connection from %" PRIu32 " port %" PRIu32, rcid, rport); - - switch (child = fork()) { - case -1: diee(EX_OSERR, "fork"); - case 0: - if (dup2(conn, STDIN_FILENO) == -1) - diee(EX_OSERR, "dup2"); - if (dup2(conn, STDOUT_FILENO) == -1) - diee(EX_OSERR, "dup2"); - if (conn != STDIN_FILENO && conn != STDOUT_FILENO) - close(conn); - execvp(argv[optind], &argv[optind]); - diee(EX_OSERR, "exec"); - } - - if (waitpid(child, NULL, 0) == -1) - diee(EX_OSERR, "waitpid"); - - close(conn); - } - diee(EX_OSERR, "poll"); + // Add `cid' and `port' arguments to binder options. + if (argz_add(&binder_opts, &binder_opts_len, "--") || + argz_add(&binder_opts, &binder_opts_len, argv[optind++]) || + argz_add(&binder_opts, &binder_opts_len, argv[optind++])) + diee(EX_OSERR, "malloc"); + + // Add all of daemon_opts onto the end of binder_opts. It's + // okay to multiply to find the size because if it would + // overflow calloc would have failed earlier. + if (argz_append(&binder_opts, &binder_opts_len, daemon_opts, daemon_opts_len)) + diee(EX_OSERR, "malloc"); + free(daemon_opts); + + // Append `prog' to binder_opts. Technically this should be + // part of daemon_opts, but then we'd just be copying it into + // one place to immediately copy it elsewhere. + for (int i = optind; i < argc; i++) + if (argz_add(&binder_opts, &binder_opts_len, argv[i])) + diee(EX_OSERR, "malloc"); + + if (verbosity == all) { + char *opt; + + // Log the full argv before we exec it. + fprintf(stderr, "%s: executing", program_invocation_short_name); + while ((opt = argz_next(binder_opts, binder_opts_len, opt))) + fprintf(stderr, " %s", opt); + fputc('\n', stderr); + } + + execzp(binder_opts, binder_opts, binder_opts_len); + diee(EX_OSERR, "execvp"); } diff --git a/vsockserver.c b/vsockserverd.c similarity index 64% copy from vsockserver.c copy to vsockserverd.c index 43307d2..1abfff9 100644 --- a/vsockserver.c +++ b/vsockserverd.c @@ -4,30 +4,25 @@ #define _GNU_SOURCE #include -#include #include #include #include +#include #include #include #include -#include -#include #include #include #include -#include - #include "env.h" #include "log.h" -#include "num.h" #include "vsock.h" noreturn static void ex_usage(void) { if (verbosity) - fprintf(stderr, "Usage: %s [ -1 ] [ -q | -Q | -v ] cid port prog...\n", + fprintf(stderr, "Usage: %s [ -1 ] [ -q | -Q | -v ] prog...\n", program_invocation_short_name); exit(EX_USAGE); } @@ -38,6 +33,8 @@ int main(int argc, char *argv[]) int opt; pid_t child; uint32_t lcid, lport, rcid, rport; + struct pollfd poll_fd = + { .fd = STDIN_FILENO, .events = POLLIN, .revents = 0 }; while ((opt = getopt(argc, argv, "+1qQv")) != -1) { switch (opt) { @@ -54,60 +51,42 @@ int main(int argc, char *argv[]) } } - // Check there are enough positional arguments (two for the - // address and at least one to exec into). - if (optind > argc - 3) + // Check that there is something for us to exec into. + if (optind > argc - 1) ex_usage(); - if (!strcmp(argv[optind], "-1")) - lcid = VMADDR_CID_ANY; - else if (getu32(argv[optind], 0, UINT32_MAX, &lcid)) - ex_usage(); - optind++; - - if (!strcmp(argv[optind], "-1")) - lport = VMADDR_PORT_ANY; - else if (getu32(argv[optind], 0, UINT32_MAX, &lport)) - ex_usage(); - optind++; - - int fd = socket(AF_VSOCK, SOCK_STREAM, 0); - if (fd == -1) - diee(EX_OSERR, "socket"); - - if (fcntl(fd, F_SETFL, O_NONBLOCK) == -1) - diee(EX_OSERR, "fcntl"); - - if (vsock_bind(fd, lcid, lport) == -1) - diee(EX_OSERR, "bind"); - - if (listen(fd, 40) == -1) - diee(EX_OSERR, "listen"); - - if (lport == VMADDR_PORT_ANY) - if (vsock_get_cid_and_port(fd, NULL, &lport) == -1) - diee(EX_OSERR, "getsockname"); + // Find out the CID and port of the socket. + if (vsock_get_cid_and_port(STDIN_FILENO, &lcid, &lport)) { + if (errno == ENOTSOCK || errno == EPROTOTYPE) + die(EX_USAGE, "stdin is not an AF_VSOCK socket"); + diee(EX_OSERR, "getsockname"); + } + // Notify the user of our port and indicate readiness. if (notify) { printf("%" PRIu32 "\n", lport); fclose(stdout); } + // Set our CID and port as environment variables so `prog' can + // know them. setenvf("VSOCKLOCALCID", 1, "%" PRIu32, lcid); setenvf("VSOCKLOCALPORT", 1, "%" PRIu32, lport); ilog("listening as %" PRIu32 " on port %" PRIu32, lcid, lport); - struct pollfd poll_fd = { .fd = fd, .events = POLL_IN, .revents = 0 }; + // Wait for a connection. while (poll(&poll_fd, 1, -1) != -1) { // On Linux, conn will be blocking. On other // platforms, this may not be the case. If other // platforms are to be supported, we'd probably want // to set O_NONBLOCK here. - int conn = vsock_accept(fd, &rcid, &rport); + int conn = vsock_accept(STDIN_FILENO, &rcid, &rport); if (conn == -1) diee(EX_OSERR, "accept"); + // Set the client's CID and port as environment + // variables so `prog' can know them. setenvf("VSOCKREMOTECID", 1, "%" PRIu32, rcid); setenvf("VSOCKREMOTEPORT", 1, "%" PRIu32, rport); @@ -116,12 +95,18 @@ int main(int argc, char *argv[]) switch (child = fork()) { case -1: diee(EX_OSERR, "fork"); case 0: + // Set up the connection socket on prog's + // stdin and stdout. This has the happy side + // effect of closing the listening socket in + // the child, since it's also on stdin. if (dup2(conn, STDIN_FILENO) == -1) diee(EX_OSERR, "dup2"); if (dup2(conn, STDOUT_FILENO) == -1) diee(EX_OSERR, "dup2"); if (conn != STDIN_FILENO && conn != STDOUT_FILENO) close(conn); + + // exec into `prog'. execvp(argv[optind], &argv[optind]); diee(EX_OSERR, "exec"); } -- 2.30.0

On Thu, Mar 18, 2021 at 08:39:31PM -0700, Cole Helbling wrote:

...

+ if (listen(fd ,40) == -1)

Minor formatting nit (comma, then space); but also, what is `40` representative of? Should this be `#define`d, or otherwise assigned to some descriptive name?

Looks like the next thing I should do after this is set up clang-tidy or something. ;) It's the backlog parameter, i.e. the minimum[1] number of connections the kernel should allow to queue up before it starts rejecting them. Would the following additional diff make you happy? :) (I won't bother resending the whole patch with it applied; for the purposes of reviewing just pretend this is part of the patch I sent.) [1]: https://utcc.utoronto.ca/~cks/space/blog/unix/ListenBacklogMeaning PS: cool thing I just discovered -- you can pipe this message to git apply, and it'll find and apply the diff (without trying to make a commit like git am would). diff --git i/vsockserver-socketbinder.c w/vsockserver-socketbinder.c index 598c01c..fdcdfa8 100644 --- i/vsockserver-socketbinder.c +++ w/vsockserver-socketbinder.c @@ -20,6 +20,8 @@ #include "num.h" #include "vsock.h" +static const int LISTEN_BACKLOG = 40; + noreturn static void ex_usage(void) { if (verbosity) @@ -71,7 +73,7 @@ int main(int argc, char *argv[]) diee(EX_OSERR, "fcntl"); if (vsock_bind(fd, cid, port) == -1) diee(EX_OSERR, "bind"); - if (listen(fd ,40) == -1) + if (listen(fd, LISTEN_BACKLOG) == -1) diee(EX_OSERR, "listen"); // Place the socket at stdout.