s6-fdholder-getdumpc fails with 'Protocol error' (EPROTO)

From: Guillermo <gdiazhartusch_at_gmail.com>
Date: Sat, 5 Aug 2017 19:12:56 -0300

Hello,

As the subject says, that is what happens on my computer. According to
the documentation:

"This is generally a programming error. It can also signal a bug in
the s6-fdholder tools, but protocol bugs have usually been wiped out
before a s6 release."

Operating system is Gentoo, architecture x64_64, GNU libc version
2.23, Linux kernel 4.9.16. Unless I made a mistake, all skarnet.org
packages are the latest versions. Steps I've taken to produce the
error:

# Start an fd-holder and store some FDs
$ s6-fdholder-daemon -i rules.d fdholder-socket &
$ mkfifo -m 0660 test-fifo
$ redirfd -rnb 0 test-fifo s6-fdholder-store fdholder-socket
fifo:/home/user/test-fifo
$ s6-ipcserver-socketbinder test-socket s6-fdholder-store
fdholder-socket unix:/home/user/test-socket
$ s6-fdholder-list fdholder-socket
fifo:/home/user/test-fifo
unix:/home/user/test-socket

#Perform a get dump
$ execlineb -Pc '
s6-fdholder-getdump fdholder-socket
pipeline { env } grep ^S6_'

s6-fdholder-getdumpc: fatal: unable to get dump: Protocol error

Partial strace (if requested I'll post it complete):

execve("/home/guillermo/skarnet/bin/s6-ipcclient",
["/home/guillermo/skarnet/bin/s6-i"..., "fdholder-socket",
"/home/guillermo/skarnet/bin/s6-f"..., "pipeline", " env", "", "grep",
"^S6_"], [/* 26 vars */]) = 0
...
socket(AF_UNIX, SOCK_STREAM, 0) = 3
connect(3, {sa_family=AF_UNIX, sun_path="fdholder-socket"}, 110) = 0
getsockname(3, {sa_family=AF_UNIX}, [110->2]) = 0
dup2(3, 6) = 6
close(3) = 0
dup2(6, 7) = 7
...
execve("/home/guillermo/skarnet/bin/s6-fdholder-getdumpc",
["/home/guillermo/skarnet/bin/s6-f"..., "pipeline", " env", "",
"grep", "^S6_"], [/* 28 vars */]) = 0
...
ppoll([{fd=6, events=POLLOUT}], 1, {tv_sec=1152921504606846976,
tv_nsec=0}, NULL, 8) = 1 ([{fd=6, revents=POLLOUT}], left
{tv_sec=1152921504606846975, tv_nsec=999996660})
sendmsg(6, {msg_name=NULL, msg_namelen=0,
msg_iov=[{iov_base="\0\0\0\1\0\0", iov_len=6}, {iov_base="?",
iov_len=1}], msg_iovlen=2, msg_controllen=0, msg_flags=0},
MSG_NOSIGNAL) = 7
recvmsg(6, {msg_namelen=0}, MSG_DONTWAIT|MSG_WAITALL|MSG_CMSG_CLOEXEC)
= -1 EAGAIN (Resource temporarily unavailable)
ppoll([{fd=6, events=POLLIN|POLLHUP}], 1, {tv_sec=1152921504606846975,
tv_nsec=999717297}, NULL, 8) = 1 ([{fd=6, revents=POLLIN}], left
{tv_sec=1152921504606846975, tv_nsec=999489651})
recvmsg(6, {msg_name=NULL, msg_namelen=0,
msg_iov=[{iov_base="\0\0\0\t\0\0\0\0\0\0\1\0\0\0\2\0\0\0P\0\2P\0\0\0Y\206;.:w\305"...,
iov_len=2047}, {iov_base=NULL, iov_len=0}], msg_iovlen=2,
msg_control=[{cmsg_len=24, cmsg_level=SOL_SOCKET,
cmsg_type=SCM_RIGHTS, cmsg_data=[3, 4]}], msg_controllen=24,
msg_flags=MSG_CMSG_CLOEXEC},
MSG_DONTWAIT|MSG_WAITALL|MSG_CMSG_CLOEXEC) = 101
close(4) = 0
close(3) = 0
writev(2, [{iov_base="s6-fdholder-getdumpc: fatal: una"...,
iov_len=64}, {iov_base=NULL, iov_len=0}], 2) = 64
exit_group(1) = ?
+++ exited with 1 +++

Looking at this it *seems* that the fd-passing part actually succeded,
and that the two received FDs are 3 and 4.

Thanks,
G.
Received on Sat Aug 05 2017 - 22:12:56 UTC