On Tue, Apr 18, 2023 at 02:59:26AM -0400, Nick Guenther wrote: > The qemu driver creates IPC sockets using absolute paths, > but under POSIX socket paths are constrained pretty tightly. > On systems with homedirs on an unusual mount point, like > network homedirs, or just particularly long usernames, this > could make starting VMs under qemu:///session impossible. > > Resolves https://gitlab.com/libvirt/libvirt/-/issues/466 Example path from that bug /home/WAVES.EXAMPLE.ORG/u123456/.config/libvirt/qemu/channel/target/domain-11-alpinelinux3.14/org.qemu.guest_agent.0 IMHO the key problem here is not your $HOME location, but rather libvirt being ridiculously verbose in the nested dir structuion Looking at the pieces * /home/WAVES.EXAMPLE.ORG/u123456 -> 31 chars $HOME, we can't change this * /.config/libvirt/qemu -> 21 chars Libvirt's config directory scope to the driver, we don't want to change this * /channel/target/domain-11-alpinelinux3.14 => 42 chars Arbitrarily inventing nesting for the sockets, we can change at will * /org.qemu.guest_agent.0 -> 23 chars Either user specified, or matches the port name, ideally don't change this So we've got 31 + 21 + 23 == 75 chars we don't want to /can't change, but that leaves 33 to play with I feel like having 'domain-' in the path is redudant as everything under /channel is for a domain. Having 'target' also feels redundant to me. We could use '/channel/tgt-11-alpinelinux3.14' == 31 chars or just /channel/11-alpinelinux3.14 == 27 chars, which gives extra scope for a longer $HOME. > > Signed-off-by: Nick Guenther <nick.guenther@xxxxxxxxxx> > --- > src/qemu/qemu_command.c | 52 ++++++++++++++++++++++++++++++++++++++--- > 1 file changed, 49 insertions(+), 3 deletions(-) > > diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c > index 4ca93bf3dc..3f180d5fb6 100644 > --- a/src/qemu/qemu_command.c > +++ b/src/qemu/qemu_command.c > @@ -53,6 +53,7 @@ > #include "virmdev.h" > #include "virutil.h" > > +#include <libgen.h> > #include <sys/stat.h> > #include <fcntl.h> > > @@ -4866,6 +4867,37 @@ qemuOpenChrChardevUNIXSocket(const virDomainChrSourceDef *dev) > struct sockaddr_un addr; > socklen_t addrlen = sizeof(addr); > int fd; > + char* wd = NULL; > + char* socket_dir_c = NULL; > + char* socket_name_c = NULL; > + char* socket_dir = NULL; > + char* socket_name = NULL; > + > + /* The path length is limited to what fits in sockaddr_un. > + * It's pretty short: 108 on Linux, and this is too easy to hit. > + * Work around this limit by using a *relative path*. > + * > + * background: https://stackoverflow.com/questions/34829600/why-is-the-maximal-path-length-allowed-for-unix-sockets-on-linux-108 > + * > + * docker added a different workaround: https://github.com/moby/moby/pull/13408 > + */ > + if ((wd = getcwd(NULL, 0)) == NULL) { > + virReportSystemError(errno, "%s", > + _("Unable to get working directory")); > + goto error; > + } > + > + socket_dir_c = strdup(dev->data.nix.path); // dirname edits the string given it, so it must be copied > + socket_name_c = strdup(dev->data.nix.path); > + > + socket_dir = dirname(socket_dir_c); > + socket_name = basename(socket_name_c); > + > + if (chdir(socket_dir) < 0) { > + virReportSystemError(errno, "%s", > + _("Unable to get change to socket directory")); > + goto error; > + } > > if ((fd = socket(AF_UNIX, SOCK_STREAM, 0)) < 0) { > virReportSystemError(errno, "%s", > @@ -4875,10 +4907,10 @@ qemuOpenChrChardevUNIXSocket(const virDomainChrSourceDef *dev) > > memset(&addr, 0, sizeof(addr)); > addr.sun_family = AF_UNIX; > - if (virStrcpyStatic(addr.sun_path, dev->data.nix.path) < 0) { > + if (virStrcpyStatic(addr.sun_path, socket_name) < 0) { > virReportError(VIR_ERR_INTERNAL_ERROR, > - _("UNIX socket path '%1$s' too long"), > - dev->data.nix.path); > + _("UNIX socket name '%1$s' too long"), > + socket_name); > goto error; > } > > @@ -4909,9 +4941,23 @@ qemuOpenChrChardevUNIXSocket(const virDomainChrSourceDef *dev) > if (virFileUpdatePerm(dev->data.nix.path, 0002, 0664) < 0) > goto error; > > + /* restore working directory */ > + if (chdir(wd) < 0) { > + virReportSystemError(errno, "%s", > + _("Unable to restore working directory")); > + goto error; > + } > + > + free(socket_name_c); > + free(socket_dir_c); > + free(wd); > + > return fd; > > error: > + if (socket_name_c != NULL) { free(socket_name_c); } > + if (socket_dir_c != NULL) { free(socket_dir_c); } > + if (wd != NULL) { free(wd); } > VIR_FORCE_CLOSE(fd); > return -1; > } > -- > 2.34.1 > With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
