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Kernel+LibC: Allow clock_gettime() to run without syscalls

This patch adds a vDSO-like mechanism for exposing the current time as
an array of per-clock-source timestamps.

LibC's clock_gettime() calls sys$map_time_page() to map the kernel's
"time page" into the process address space (at a random address, ofc.)
This is only done on first call, and from then on the timestamps are
fetched from the time page.

This first patch only adds support for CLOCK_REALTIME, but eventually
we should be able to support all clock sources this way and get rid of
sys$clock_gettime() in the kernel entirely. :^)

Accesses are synchronized using two atomic integers that are incremented
at the start and finish of the kernel's time page update cycle.
This commit is contained in:
Andreas Kling 2021-08-10 13:44:01 +02:00
parent f02d73db4d
commit fdfc66db61
7 changed files with 117 additions and 0 deletions

View file

@ -412,6 +412,7 @@ public:
KResultOr<FlatPtr> sys$anon_create(size_t, int options);
KResultOr<FlatPtr> sys$statvfs(Userspace<const Syscall::SC_statvfs_params*> user_params);
KResultOr<FlatPtr> sys$fstatvfs(int fd, statvfs* buf);
KResultOr<FlatPtr> sys$map_time_page();
template<bool sockname, typename Params>
int get_sock_or_peer_name(const Params&);