On Thu, Aug 22, 2024 at 10:09:56PM +0300, Peter Pentchev wrote: > On Thu, Aug 22, 2024 at 05:06:53PM +0200, Florian Weimer wrote: > > * Lennart Poettering: > > > > > On Mi, 07.08.24 13:09, Vít Ondruch (vondruch@xxxxxxxxxx) wrote: > > > > > >> With new RPM, I hit the limit in two packages: > > >> > > >> https://koschei.fedoraproject.org/package/rubygem-abrt > > >> > > >> https://koschei.fedoraproject.org/package/rubygem-pg > > >> > > >> > > >> I have read: > > >> > > >> https://unix.stackexchange.com/questions/367008/why-is-socket-path-length-limited-to-a-hundred-chars > > >> > > >> https://stackoverflow.com/questions/34829600/why-is-the-maximal-path-length-allowed-for-unix-sockets-on-linux-108 > > >> > > >> > > >> But I still wonder why we should live with such limitation in 21st century. > > > > > > You don't really have to live with such a limitation. In systemd we > > > have code that works around this limitation via O_PATH. i.e. when > > > connect()ing you first open the socket inode with O_PATH, and then you > > > fire the connect() specifying /proc/self/fd/<fd> as path. That always > > > fits into the 108ch limit. > > > > Do you think this is useful more generally? What about opening files > > with names longer than PATH_MAX? > > > > > bind()ing to an overly long unix socket path is also doable, but > > > harder (since you cannot O_PATH on an inode that doesn't exist > > > yet). The way I'd do it is via chdir() to the dir of the target path > > > and binding to a relative path then. But chdir() is of course icky, > > > since it's a global property of a process, hence will affect all > > > threads. Hence, maybe do this in a short-lived forked off process. > > > > I would have expected that it's possible to use a directory descriptor > > under /proc/self/fd as the base, but that doesn't seem to work for some > > reason. > > I think the reason is O_PATH - bind(2) is not among the syscalls that > it is documented to allow. However, see the attached program that > creates a subdirectory with a long name in the current working > directory, opens it without O_PATH, but with O_DIRECTORY, and then > binds a Unix-domain socket to /proc/self/fd/N; it works for me at > least on Debian testing and a month-or-two-old Fedora pre-42 Rawhide. > ("Works for me" in the sense that "cd this-...; nc -v -U meow" says > that it has connected to the Unix-domain socket; of course, the program > does not attempt to communicate with connected clients) ...and of course I forgot to attach the program, did I not... > > You could also use a long-lived service thread that has called > > unshare(CLONE_FS), so that it has its own current directory. This is a > > bit iffy because glibc won't know about it, but it's already used by > > some popular file servers, so it should be okay. I've posted a patch > > that implements a proper NPTL facility for this, but it met with a > > surprising amount of resistance. I suppose I could dust it off and > > repost it. > > That might actually work, yeah. > > G'luck, > Peter > > -- > Peter Pentchev roam@xxxxxxxxxxx roam@xxxxxxxxxx peter@xxxxxxxxxxxxxx > PGP key: https://www.ringlet.net/roam/roam.key.asc > Key fingerprint 2EE7 A7A5 17FC 124C F115 C354 651E EFB0 2527 DF13 > -- > _______________________________________________ > devel mailing list -- devel@xxxxxxxxxxxxxxxxxxxxxxx > To unsubscribe send an email to devel-leave@xxxxxxxxxxxxxxxxxxxxxxx > Fedora Code of Conduct: https://docs.fedoraproject.org/en-US/project/code-of-conduct/ > List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines > List Archives: https://lists.fedoraproject.org/archives/list/devel@xxxxxxxxxxxxxxxxxxxxxxx > Do not reply to spam, report it: https://pagure.io/fedora-infrastructure/new_issue -- -- Peter Pentchev roam@xxxxxxxxxxx roam@xxxxxxxxxx peter@xxxxxxxxxxxxxx PGP key: https://www.ringlet.net/roam/roam.key.asc Key fingerprint 2EE7 A7A5 17FC 124C F115 C354 651E EFB0 2527 DF13
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/un.h>
#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#define DIRNAME "this-is-a-directory-with-a-really-long-name-and-stuff-and-such-and-stuff-and-such-and-stuff-and-such-and-stuff-and-such"
#define SLEEP_TIME 120
int main(void)
{
puts("Hell world");
printf("Trying to create a directory if it does not exist: %s\n", DIRNAME);
if (mkdir(DIRNAME, 0755) == -1 && errno != EEXIST)
err(1, "mkdir");
const int dirfd = open(DIRNAME, O_RDONLY | O_DIRECTORY);
if (dirfd == -1)
err(1, "open");
printf("got dirfd %d\n", dirfd);
const int sock = socket(AF_UNIX, SOCK_STREAM, 0);
if (sock == -1)
err(1, "socket");
struct sockaddr_un sun = { 0 };
sun.sun_family = AF_UNIX;
snprintf(sun.sun_path, sizeof(sun.sun_path), "/proc/self/fd/%d/meow", dirfd);
printf("Trying to bind to %s\n", sun.sun_path);
if (bind(sock, (const struct sockaddr *)&sun, sizeof(sun)) == -1)
err(1, "bind");
puts("uh... got it?");
printf("Trying to listen on socket %d\n", sock);
if (listen(sock, 10) == -1)
err(1, "listen");
printf("sleeping for %u seconds\n", SLEEP_TIME);
sleep(SLEEP_TIME);
puts("shutting down");
return 0;
}
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