[Libguestfs] [nbdkit PATCH] log: Allow user option of appending to log

Always truncating a log can wipe out useful history. Add an option to change this. Signed-off-by: Eric Blake <eblake(a)redhat.com&gt; --- Hmm - logappend=false enables appending. Maybe we need a common utility function for parsing bool values (parse 0 and case-insensitive "off" or "false" as off, all others as true, or even report values that can't be parsed reasonably) filters/log/nbdkit-log-filter.pod | 5 +++-- filters/log/log.c | 8 +++++++- tests/test-log.sh | 6 +++++- 3 files changed, 15 insertions(+), 4 deletions(-) diff --git a/filters/log/nbdkit-log-filter.pod b/filters/log/nbdkit-log-filter.pod index 0903329..88b9f9b 100644 --- a/filters/log/nbdkit-log-filter.pod +++ b/filters/log/nbdkit-log-filter.pod @@ -4,7 +4,7 @@ nbdkit-log-filter - nbdkit log filter =head1 SYNOPSIS - nbdkit --filter=log plugin logfile=FILE [plugin-args...] + nbdkit --filter=log plugin logfile=FILE [logappend=VAL] [plugin-args...] =head1 DESCRIPTION @@ -22,7 +22,8 @@ work even when nbdkit is run as a daemon. The nbdkit-log-filter requires a single parameter C<logfile> which specifies the path of the file to use for logging. If the file -already exists, it will be truncated. +already exists, it will be truncated unless the C<logappend> parameter +was specified with any non-empty value other than "0". =head1 EXAMPLES diff --git a/filters/log/log.c b/filters/log/log.c index 2079084..e6ed3b4 100644 --- a/filters/log/log.c +++ b/filters/log/log.c @@ -43,6 +43,7 @@ #include <pthread.h> #include <sys/time.h> #include <assert.h> +#include <stdbool.h> #include <nbdkit-filter.h> @@ -51,6 +52,7 @@ static uint64_t connections; static char *logfilename; static FILE *logfile; +static bool append; static pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER; static void @@ -75,6 +77,10 @@ log_config (nbdkit_next_config *next, void *nxdata, } return 0; } + if (strcmp (key, "logappend") == 0) { + append = value[0] && (value[0] != '0' || value[1]); + return 0; + } return next (nxdata, key, value); } @@ -86,7 +92,7 @@ log_config_complete (nbdkit_next_config_complete *next, void *nxdata) nbdkit_error ("missing logfile= parameter for the log filter"); return -1; } - logfile = fopen (logfilename, "w"); + logfile = fopen (logfilename, append ? "a" : "w"); if (!logfile) { nbdkit_error ("fopen: %m"); return -1; diff --git a/tests/test-log.sh b/tests/test-log.sh index f0eacb7..b30d20e 100755 --- a/tests/test-log.sh +++ b/tests/test-log.sh @@ -45,7 +45,9 @@ if ! qemu-io -f raw -c 'w 1M 2M' log.img; then fi # Run nbdkit with logging enabled to file. -start_nbdkit -P log.pid -U log.sock --filter=log file log.img logfile=log.log +echo '# My log' > log.log +start_nbdkit -P log.pid -U log.sock --filter=log file log.img \ + logfile=log.log logappend=1 # For easier debugging, dump the final log files before removing them # on exit. @@ -61,6 +63,8 @@ cleanup_fn cleanup qemu-io -f raw -c 'w -P 11 1M 2M' 'nbd+unix://?socket=log.sock' qemu-io -r -f raw -c 'r -P 11 2M 1M' 'nbd+unix://?socket=log.sock' +# The log should have been appended, preserving our marker. +grep '# My log' log.log # The log should show a write on connection 1, and read on connection 2. grep 'connection=1 Write id=1 offset=0x100000 count=0x200000 ' log.log grep 'connection=2 Read id=1 offset=0x200000 count=0x100000 ' log.log -- 2.17.2