Re: [Libguestfs] [libnbd PATCH] info: Try harder for graceful disconnect from server

There are a number of ways in which gathering information can fail. But when possible, it makes sense to let the server know that we are done talking, as it minimizes the likelihood that nbdinfo's error message will be obscured by an accompanying error message by the server complaining about an unclean disconnect. For example, with a one-off qemu temporarily patched as mentioned in commit 0f8ee8c6 to advertise sizes larger than 2^63, kicking off 'qemu-nbd -f raw -r file &' produces: pre-patch: $ ./run nbdinfo --size nbd://localhost /home/eblake/libnbd/info/.libs/nbdinfo: nbd_get_size: server claims size 9223372036854781440 which does not fit in signed result: Value too large for defined data type qemu-nbd: option negotiation failed: Failed to read opts magic: Unexpected end-of-file before all data were read

post-patch: $ ./run nbdinfo --size nbd://localhost /home/eblake/libnbd/info/.libs/nbdinfo: nbd_get_size: server claims size 9223372036854781440 which does not fit in signed result: Value too large for defined data type if nbdinfo is run in the same terminal as qemu-nbd. Signed-off-by: Eric Blake <eblake(a)redhat.com&gt; --- info/main.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/info/main.c b/info/main.c index c8248c61..05f19f43 100644 --- a/info/main.c +++ b/info/main.c @@ -88,6 +88,17 @@ usage (FILE *fp, int exitcode) exit (exitcode); } +void +clean_shutdown (void) +{ + /* If we are connected but detect an error, try to give the server + * notice that we are done talking. Ignore failures, as this is + * only a courtesy measure. + */ + if (nbd) + nbd_shutdown (nbd, 0); +} + int main (int argc, char *argv[]) { @@ -277,6 +288,7 @@ main (int argc, char *argv[]) fprintf (stderr, "%s: %s\n", progname, nbd_get_error ()); exit (EXIT_FAILURE); } + atexit (clean_shutdown); nbd_set_uri_allow_local_file (nbd, true); /* Allow ?tls-psk-file. */ /* Set optional modes in the handle. */ @@ -353,6 +365,7 @@ main (int argc, char *argv[]) free_exports (); nbd_shutdown (nbd, 0); nbd_close (nbd); + nbd = NULL; /* Close the output stream and copy it to the real stdout. */ if (fclose (fp) == EOF) { -- 2.41.0