3 nbdkit-log-filter - nbdkit log filter
7 nbdkit --filter=log PLUGIN
8 [logfile=FILE | logscript=SCRIPT] [logappend=BOOL]
13 C<nbdkit-log-filter> is a filter that logs all transactions to a file
16 When used as the first filter, it can show the original client
17 requests. As a later filter, it can show how earlier filters have
18 modified the original request.
20 When using C<logfile=FILE>, logs are written to a log file with the
21 format described in L</LOG FILE FORMAT> below.
23 When using C<logscript=SCRIPT>, logs invoke the external script. See
26 An alternative to this filter is simply to run nbdkit with the I<-f>
27 and I<-v> flags which enable verbose debugging to stderr. This logs
28 many aspects of nbdkit operation, but requires running nbdkit in the
29 foreground. The log filter uses a more parsimonious and more easily
30 parsable format and works when nbdkit runs in the background.
34 C<logfile> or C<logscript> or both can be given. If neither then the
41 The file where the log is written. See L</LOG FILE FORMAT> below.
43 =item B<logscript=>SCRIPT
47 Log lines invoke an external script. See L</LOG SCRIPT> below.
49 =item B<logappend=true>
51 =item B<logappend=false>
55 This only affects C<logfile>. If C<false> (the default), if the file
56 already exists it will be truncated. If C<true>, the filter appends
57 to the existing log file.
63 Serve the file F<disk.img>, and log each client transaction in the
66 nbdkit --filter=log file disk.img logfile=disk.log
68 Repeat the task, but with the cow (copy-on-write) filter to perform
69 local caching of data served from the original plugin:
71 nbdkit --filter=cow --filter=log file disk.img logfile=disk.log2
73 After running a client that performs the same operations under each of
74 the two servers, you can compare F<disk.log> and F<disk.log2> to see
75 the impact of the caching.
77 =head1 LOG FILE FORMAT
79 An example logging session of a client that requests an export list
80 before performing a single successful read is:
82 2020-08-06 02:07:23.080415 ListExports id=1 readonly=0 tls=0 ...
83 2020-08-06 02:07:23.080502 ...ListExports id=1 exports=("") return=0
84 2020-08-06 02:07:23.080712 connection=1 Connect export="" tls=0 size=0x400 minsize=0x1 prefsize=0x200 maxsize=0xffffffff write=1 flush=1 rotational=0 trim=1 zero=2 fua=2 extents=1 cache=2 fast_zero=1
85 2020-08-06 02:07:23.080907 connection=1 Read id=1 offset=0x0 count=0x200 ...
86 2020-08-06 02:07:23.080927 connection=1 ...Read id=1 return=0
87 2020-08-06 02:07:23.081255 connection=1 Disconnect transactions=1
89 All lines start with a timestamp in C<YYYY-MM-DD HH:MM:ZZ.MS> format.
91 For connected calls, C<connection=N> is present to distinguish
94 The action follows. Currently the following actions are logged:
95 ListExports, Ready, Fork, Preconnect, Connect, Read, Write, Zero,
96 Trim, Extents, Cache, Flush and Disconnect.
98 Some actions are logged across two lines showing the call and return
99 value. Because nbdkit handles requests in parallel different requests
100 may be intermingled. Use the C<id=N> field for correlation, it is
101 unique per connection.
103 Strings and lists are shell-quoted.
107 If C<logscript=SCRIPT> is given on the command line then log entries
108 are passed to the external script.
110 The script is passed several shell variables:
116 The action name, like C<"Read">, C<"Write"> etc.
120 The connection ID identifying the client, only for connected calls
125 For messages of type C<"LEAVE"> which fail (C<$return = -1>), this
126 contains the errno as a string, for example C<"EIO">.
130 The transaction ID, used to correlate actions which are split into two
131 messages C<"ENTER"> and C<"LEAVE">.
135 For messages of type C<"LEAVE"> this is the return code, usually C<0>
136 for success and C<-1> if there was an error.
140 The message type: C<"ENTER">, C<"LEAVE"> or C<"PRINT">.
142 =item other shell variables
144 Other parameters like C<offset=N> are turned into shell variables
149 Note the return value of the script is ignored. Log scripts cannot
150 modify or interrupt request processing.
152 =head2 Log script examples
156 nbdkit -f --filter=log null 10M \
157 logscript='echo $connection $type $id $act $offset >&2'
159 might print lines like:
163 1 ENTER 2 Write 0x200
167 corresponding to log file lines:
170 connection=1 Read id=1 offset=0x0 count=0x200 ...
171 connection=1 Write id=2 offset=0x200 count=0x200 ...
172 connection=1 ...Write id=2
173 connection=1 ...Read id=1
175 This script will trigger a message when any client reads:
177 nbdkit -f --filter=log memory 10M \
179 if [ "$act" = "Read" -a "$type" = "ENTER" ]; then
180 echo Client is reading $count bytes from $offset >&2
188 =item C<logfile=FILE> parameter
190 This filter writes to the file specified by the C<logfile=FILE>
193 =item F<$filterdir/nbdkit-log-filter.so>
197 Use C<nbdkit --dump-config> to find the location of C<$filterdir>.
203 C<nbdkit-log-filter> first appeared in nbdkit 1.4.
208 L<nbdkit-file-plugin(1)>,
209 L<nbdkit-cow-filter(1)>,
211 L<nbdkit-stats-filter(1)>.