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Pantavisor Log sockets

The Pantavisor logging system works with 2 sockets pv-ctrl-log, for receive logs from any application who needs to send logs to Pantavisor log system, and pv-fd-log used by Pantavisor to subscribe file descriptors (fd) to be reading and add to the log system as appropriate.


All messages are sent to the pv-ctrl-log socket inside a structure called logserver_msg, defined as follows:

struct logserver_msg {
    int version;
    int len;
    char buffer[0];

The fields in the structure are:

  • version: always 0 (no other version exists currently)
  • len: length of the buffer
  • buffer: log data. This data is organized in a simple way using 0 as separator:


  • level: log level for the message, a numeric value. See below.
  • platform: container name
  • source: specific place where the log belongs (e.g: function name, module, etc)
  • data: message to log

The log levels are defined using an enum:

enum log_level {
    FATAL, // 0
    ERROR, // 1
    WARN,  // 2
    INFO,  // 3
    DEBUG, // 4
    ALL    // 5


Pantavisor provides a Unix socket to add and remove a fd. Those fd will be polling and if there are data available it will be added to the system.


For the subscription mechanism sendmsg system call must be used. This function is present on several languages like C and C++, Go, Rust and Python, among others.

As part of the protocol, the platform (container name) and the source of the fd (e.g. console.log, syslog, etc.) must be specified in the header of the message, using the iov structure, where iov[0] has the platform and the iov[1] contains the source, each field have a maximum of 50 characters length.

Once added, Pantavisor creates a file using the platform and source files inside the /pantavisor/logs/current/ directory. For example, if the platform is Foo and the source is var/log/Bar.log then the directory /pantavisor/logs/current/Foo/var/log/Bar.log will be created.

Only one file descriptor can be subscribed using a specific pair platform-source, where platform refers to the container where the logs belong and the src denote where the log is originated (e.g: console.log)


To unsubscribe a fd a new call to sendmsg must be done with fd = -1 using the pair platform-source to identify the fd.