CA-116448: Don't die by writing to mem address 0x0, call abort() instead.

Signed-off-by: Thanos Makatos <thanos.makatos@citrix.com>
Reviewed-by: Vineeth Thampi Raveendran <vineeth.thampi@citrix.com>

GitHub: closes #56 on xapi-project/blktap
CA-113543: Don't spam syslog for benign request failures.

This was most likely a debug print added when the NBD funcionality was
implemented. tapdisk either way complains about failed requests
elsewhere.

Signed-off-by: Thanos Makatos <thanos.makatos@citrix.com>
Acked-by: Germano Percossi <germano.percossi@citrix.com>

GitHub: closes #59 on xapi-project/blktap
CA-120823: Don't use a tmp file for logging and handle SIGHUP

tapdisk now handles the SIGHUP signal, closing and opening the log file
in order to allow logrotate to rotate the log file.

Signed-off-by: Thanos Makatos <thanos.makatos@citrix.com>
Reviewed-by: Germano Percossi <germano.percossi@citrix.com>

GitHub: closes #61 on xapi-project/blktap
CP-6999: Allow coalescing to out-of-chain parents.

Signed-off-by: Thanos Makatos <thanos.makatos@citrix.com>
Reviewed-by: Keith Petley <keith.petley@citrix.com>

GitHub: closes #63 on xapi-project/blktap