Net-snmp code analysis: fd_event_manager.c

The fd_event_manager.c module is used to manage read, write, and abnormal file descriptors.

Directory/net-snmp-5.4.2.1/snmplib/fd_event_manager.c

 

Used to store three different types of descriptors

Int external_readfd [num_external_fds], external_readfdlen = 0;
Int external_writefd [num_external_fds], external_writefdlen = 0;
Int external_effectfd [num_external_fds], external_effectfdlen = 0;

 

Stores the processing functions corresponding to the three descriptors.
Void (* external_readfdfunc [num_external_fds]) (INT, void *);
Void (* external_writefdfunc [num_external_fds]) (INT, void *);
Void (* external_effectfdfunc [num_external_fds]) (INT, void *);

Storage data to be processed

Void * external_readfd_data [num_external_fds];
Void * external_writefd_data [num_external_fds];
Void * external_exceptfd_data [num_external_fds];

 

Static int external_fd_unregistered;

 

It is equivalent to three initialization functions. The parameters in the functions are assigned to the above data structure respectively.

Int
Register_readfd (int fd, void (* func) (INT, void *), void * Data)

Int
Register_writefd (int fd, void (* func) (INT, void *), void * Data)

Int
Register_effectfd (int fd, void (* func) (INT, void *), void * Data)

 

 

Deletes the specified file descriptor from the data structure.

Int
Unregister_readfd (int fd)

Int
Unregister_writefd (int fd)

Int
Unregister_exceptfd (int fd)

 

Add the file descriptor registered in the data structure to the corresponding file descriptor set

Void netsnmp_external_event_info (int * numfds, fd_set * readfds, fd_set * writefds, fd_set * limit TFDs)

Test whether the file descriptor in the data structure is added to the corresponding file descriptor set and the corresponding function is called for processing.

Void netsnmp_dispatch_external_events (int * count, fd_set * readfds, fd_set * writefds, fd_set * limit TFDs)