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#ifndef _EPOCH_H
#define _EPOCH_H
#include <stdint.h>
/*
* Each node is timestamped with its starting epoch.
* After each relevant operation the timestamp is updated.
*
* Epoch is the key concept for layered virtualization.
* each system call request generated inside the hypervisor
* (guardian angels, helper threads) happens at the epoch
* when that virtualization was activated (e.g. the epoch
* when a file system was mounted). In this way these system
* calls see the world at that time, and cen be further
* virtualized.
*
* e.g. mount a file system in /mnt at epoch 42
* mount the file system image /mnt/image on /mnt at epoch 44
* open (/mnt/myfile) at epoch 50.
* /mnt/myfile is in the subtree virtualized by the mount at epoch 44.
* the virtualization module (e.g. vufuse) processing the 'open' request
* runs at epoch 44, so if it needs to run a system call (say
* lstat("/mnt/test"...), the request is managed by the virtualization
* aptivated by the "mount" at epoch 42 (at epoch 44 the second "mount"
* did not exist).
*/
typedef uint64_t epoch_t;
/* function definitions */
/* a relevant event happened. epoch is incremented by one tick */
void update_vepoch(void);
/* define a new working/virtual epoch for the current thread,
it returns the previous epoch (to restore the value in a second time */
epoch_t set_vepoch(epoch_t e);
/* return the working/virtual epoch for the current thread, */
epoch_t get_vepoch(void);
/* return the current (global) epoch, the *now* epoch */
epoch_t get_epoch(void);
/* set the current (global) epoch, to the current/global/ *now* epoch */
epoch_t update_epoch(void);
/* return the service_epoch if it is consistent with the current
working/virtual epoch of calling thread.
It returns 0 if service_epoch is too new, so this
'service'/virtualization did not exist at the current/working/virtual epoch */
epoch_t matching_epoch(epoch_t service_epoch);
#endif
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