Pantavisor Log Sockets

The Pantavisor logging system uses two Unix sockets for inter-process log management: pv-ctrl-log for receiving direct log messages and pv-fd-log for subscribing file descriptors to be polled by Pantavisor.

pv-ctrl-log

This socket is used by applications and containers to send log messages directly to the Pantavisor Log Server. All messages must follow the logserver_msg structure:

struct logserver_msg {
    int code; // Protocol code: 0 for LEGACY, 256 for CMD
    int len;  // Length of the following buffer
    char buf[0]; // Log data buffer
};

Legacy Protocol (code = 0)

The buf contains the log metadata and message, separated by null terminators (\0):

level\0platform\0source\0data

• level: Log level as a string (e.g., "3" for INFO).
• platform: Name of the container or "pantavisor".
• source: The specific source of the log (e.g., a process name or module).
• data: The actual log message content.

The supported log levels are: * 0: FATAL * 1: ERROR * 2: WARN * 3: INFO * 4: DEBUG * 5: ALL

pv-fd-log

This socket allows containers to delegate the polling of their file descriptors (e.g., pipes, sockets, or open files) to Pantavisor.

Subscription Protocol

To subscribe or unsubscribe a file descriptor, you must use the sendmsg system call with SCM_RIGHTS to pass the file descriptor.

The msghdr must contain an iovec array with 4 elements:

iov Index	Type	Max Length	Description
iov[0]	string	50 bytes	Platform name (container name)
iov[1]	string	50 bytes	Source name (e.g., "stdout", "syslog")
iov[2]	int	4 bytes	Log level for the messages from this FD
iov[3]	int	4 bytes	Action: 1 to subscribe, 0 to unsubscribe

Subscribe

• Send the file descriptor using SCM_RIGHTS.
• Set iov[3] to 1.
• Pantavisor will poll this FD and create a corresponding log file at /storage/logs/current/<platform>/<source>.

Unsubscribe

• Set iov[3] to 0.
• The file descriptor passed in SCM_RIGHTS can be -1.
• Pantavisor will stop polling and close its internal reference to the FD for that platform/source pair.

Note

Only one file descriptor can be subscribed per platform-source pair. Subscribing a new FD for an existing pair will replace the previous one.