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/*
* kernel/servers.h
*/
#define SRTT_BETA 990
#define SRTT_BETA_COMP 10
#define SRTT_BETA_BASE 1000
/*
* Though presented as a 16-bit number in sysfs, the SRTT is stored in
* an unsigned long, SRTT_SHIFT bits left-shifted. This helps
* preserve the precision we need tou update the SRTTs. If we stored
* SRTT in an integer, it would only be changed by RTTS *very* far
* away from it.
*/
#define SRTT_SHIFT 10
/*
* After this interval without answering
* requests a server is considered down.
*/
#define TIMEOUT_STALLED 3*HZ
/*
* Configure @srv_info based on @server: Create a socket, connect it
* and start a dnbd2_rx_loop for it.
*/
int add_server(dnbd2_server_t server, struct srv_info *srv_info);
/*
* Reset @srv_info: Stop dnbd2_rx_loop, close the socket and zero all
* variables.
*/
void del_server(struct srv_info *srv_info);
/*
* Look for an unused server-slot in @dev and configure it according
* to @server (using add_server). Nothing happens if the list of
* servers if full or if there is already a server in the list with
* the same IP and port as @server.
*/
void try_add_server(dnbd2_server_t server, dnbd2_device_t *dev);
/*
* This function enqueues into the send-queue a request for the device
* capacity (CMD_GET_SIZE). This type of request is retransmitted
* every second. If an answer doesn't arrive within 4 seconds it
* assumes that the server is down.
*/
sector_t srv_get_capacity(struct srv_info *srv_info);
/*
* Update min, max and srtt in @srv_info.
*/
void update_rtt(uint16_t rtt, struct srv_info *srv_info, uint16_t cmd);
/*
* Enqueue a heartbeat request (CMD_GET_SERVERS) for @srv_info into
* the send-queue.
*/
void enqueue_hb(struct srv_info *srv_info);
/*
* Schedule the removal of @srv_info to be processed by the global
* kernel workqueue as soon as possible. This function allows to
* trigger the removal of servers from within timers, in which
* sleeping is not allowed.
*/
void schedule_del_server(struct srv_info *srv_info);
/*
* Schedule the search for a faster server:
* 1. Detect if the active server is stalled (down). In this case
* switch to another server, if possible, and remove the old one
* from the list. If no servers are available to switch to
* start the emergency mode.
* 2. If the emergency mode was not started go through the list of
* servers and pick the one with the smallest SRTT. If this
* server meets our requirements (to_jiffies and to_percent)
* switch to it.
*/
void schedule_activate_fastest(dnbd2_device_t *dev);
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