On Thu, Feb 05, 2015 at 09:24:32AM +0100, Robert Baldyga wrote:
> No, function/f_fs.c and legacy/inode.c are in class (1). They have
> datagram semantics - each vector element is submitted in separate USB
> request. Each single request is sent in separate USB data packet (for
> bulk endpoints it can be more than one packet). In fact sync
> read()/write() also will give different results while called once with
> some block of data or in loop with the same block of data splitted into
> a few parts.
No, they don't. This is from ffs_epfile_io():
data = kmalloc(data_len, GFP_KERNEL);
if (unlikely(!data))
return -ENOMEM;
if (io_data->aio && !io_data->read) {
int i;
size_t pos = 0;
for (i = 0; i < io_data->nr_segs; i++) {
if (unlikely(copy_from_user(&data[pos],
io_data->iovec[i].iov_base,
io_data->iovec[i].iov_len))) {
ret = -EFAULT;
goto error;
}
pos += io_data->iovec[i].iov_len;
}
and that's the last point where it looks at iovec. After that all work
is done to the copy in data, where no information about the boundaries
survives. And ep_aio_write() (in legacy/inode.c) is the same way.
You are confusing datagram-per-syscall (which they are) with
datagram-per-iovec (which they are definitely not). IOW, they behave
as UDP sockets - writev() is purely scatter-gather variant of write(),
with datagram per syscall and all vector elements silently concatenated.
That's class 2, and _not_ in its intersection with class 1.
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