Re: [Libguestfs] [PATCH libnbd] info: Write output atomically.

If the server fails, nbdinfo can write partial output before the error message (albeit on different channels). Here is an example: $ nbdkit eval open='echo EIO fail >&2; exit 1' --run 'nbdinfo --json "$uri"' { "protocol": "newstyle-fixed", "TLS": false, nbdkit: eval[1]: error: /tmp/nbdkitii3pZW/open: fail nbdkit: eval[1]: error: /tmp/nbdkitii3pZW/open: fail nbdinfo: nbd_opt_go: server replied with error to opt_go request: No such file or directory Notice the partial JSON document, and the error message from nbdinfo. With this commit nbdinfo tries to produce either the complete output or the error message. --- info/Makefile.am | 1 + info/info-atomic-output.sh | 32 ++++++ info/nbdinfo.c | 194 ++++++++++++++++++++++--------------- 3 files changed, 147 insertions(+), 80 deletions(-)

+++ b/info/info-atomic-output.sh @@ -0,0 +1,32 @@

+. ../tests/functions.sh + +set -e +set -x + +requires nbdkit --version +requires nbdkit eval --version

+ +out=info-atomic-output.out +cleanup_fn rm -f $out + +nbdkit -U - eval open='echo EIO fail >&2; exit 1' \ + --run '$VG nbdinfo --size "nbd+unix:///?socket=$unixsocket"' > $out ||: