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School of Computer Science & Engineering
University of New South Wales
 Advanced Operating Systems 
 COMP9242 2002/S2 

Timeouts...

• IPC timeouts can be specified between 1s and 19h
• page fault timeouts can be specified between 4s (1ms) and 256s

However, actual timeout resolution is generally more coarse:
1ms timeout resolution on MIPS

Data structure l4/types.h:l4_timeout_t, L4_IPC_TIMEOUT()

Utilities (time.h):

void l4_mips_encode_timeout(dword_t msecs, byte_t *mant,
                            byte_t *exp, byte_t round);
dword_t l4_mips_decode_timeout(byte_t mant, byte_t exp);

And similar for page-fault timeouts.

Page fault in receiver's AS results in RPC using sender's send pagefault timeout.

Pagefault in sender's AS results in RPC using receiver's receive pagefault timeout.

Page fault timeouts are required for security.

They ensure that an untruted server cannot install a non-existing page fault handler, which would then lead to the IPC blocking indefinitively, if it triggers a page fault.