* the first one would cause an unnecessary malloc() of iovec storage for
a msg_iovlen of UIO_SMALLIOV although the required amount of memory has
been allocated on the stack.
* the second one would cause a recvmsg() or sendmsg() with a msg_iovlen of
UIO_MAXIOV to fail with EMSGSIZE, which is also a violation of XNS5.
* availability of POSIX Synchronized I/O (kern.synchronized_io),
* maximum number of iovec structures to be used in readv(2) etc. (kern.iov_max)
via sysctl().
* if synchronized I/O file integrity completion of read operations was
requested, set IO_SYNC in the ioflag passed to the read vnode operator.
* if synchronized I/O data integrity completion of write operations was
requested, set IO_DSYNC in the ioflag passed to the write vnode operator.
means we're in interrupt context. Since we can be called from a network
hardware interrupt, we could corrupt the protocol queues we try to drain
them at that time.
called when devices attach, take two.
Note that it is necessary that mbinit() NOT allocate memory, since it
is called before mb_map is created. This is not a problem with the
pool allocator that is now used for mbufs and mbuf clusters.
The read/write system calls return ssize_t because -1 is used to indicate
error, therefore the transfer size MUST be limited to SSIZE_MAX, otherwise
garbage can be returned to the user.
There is NO change from existing behavior here, only a more precise
definition of that the semantics are, except in the Alpha case, where
the full SSIZE_MAX transfer size can now be realized (ssize_t is 64-bit
on the Alpha).
The read/write system calls return ssize_t because -1 is used to indicate
error, therefore the transfer size MUST be limited to SSIZE_MAX, otherwise
garbage can be returned to the user.
There is NO change from existing behavior here, only a more precise
definition of that the semantics are, except in the Alpha case, where
the full SSIZE_MAX transfer size can now be realized (ssize_t is 64-bit
on the Alpha).
- If either an alloc or release function is provided, make sure both are
provided, otherwise panic, as this is a fatal error.
- If using the default allocator, default the pool pagesz to PAGE_SIZE,
since that is the granularity of the default allocator's mechanism.
- In the default allocator, use new functions:
uvm_km_alloc_poolpage()/uvm_km_free_poolpage(), or
kmem_alloc_poolpage()/kmem_free_poolpage()
rather than doing it here. These functions may use pmap hooks to
provide alternate methods of mapping pool pages.
pk