[Libguestfs] [libnbd PATCH 1/4] examples: aio-connect-read.c: Fix error handling

This example failed to check the *error parameter to the read completion callback. Although the buffers in this example start life zero-initialized due to living in .bss (so there is no leak of heap contents), later reads could repeat the decoding of a buffer returned from an earlier read rather than reporting the failure. Fixed by reporting the error and exiting early. Here is an example failure fixed by this patch: $ ./run nbdkit -U - eval get_size='echo 64k' pread='echo EIO >&2; exit 1' \ --run 'examples/aio-connect-read $unixsocket' nbdkit: eval[1]: error: /tmp/nbdkit5kfDY2/pread: failed to read: Input/output error nbdkit: eval[1]: error: /tmp/nbdkit5kfDY2/pread: nbdkit: eval[1]: error: write error reply: Broken pipe $ echo $? 1 which previously dumped 64k of all zeroes before exiting with status 0. --- examples/aio-connect-read.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/examples/aio-connect-read.c b/examples/aio-connect-read.c index 799525ad..26ac3f99 100644 --- a/examples/aio-connect-read.c +++ b/examples/aio-connect-read.c @@ -17,6 +17,7 @@ #include <stdlib.h> #include <stdint.h> #include <inttypes.h> +#include <errno.h> #include <assert.h> #include <libnbd.h> @@ -35,6 +36,12 @@ hexdump (void *user_data, int *error) struct data *data = user_data; FILE *pp; + if (*error) { + errno = *error; + perror ("failed to read"); + exit (EXIT_FAILURE); + } + printf ("sector at offset 0x%" PRIx64 ":\n", data->offset); pp = popen ("hexdump -C", "w"); -- 2.34.1