Re: SSH FTP - 6.1 Request Synchronization and Reordering

[Simon Tatham <anakin%pobox.com@localhost>]

Tobias Ringstrom  <tori%ringstrom.mine.nu@localhost> wrote:
> Reading the first paragraph, it is easy to get the impression that
> read/write requests to the same file cannot be reordered, not the
> responses.

But both are true, though, surely?

If I submit a read request covering bytes 0-100, then a write
request covering bytes 20-120, and then a read request covering
bytes 40-140, then _both_ the following restrictions apply:

 (a) The requests may not be processed in a (perceptibly) different
     order. That is, the first read must be performed before the
     write (so that it returns the unmodified pre-write data) and
     the second read must be performed after the write (so that it
     returns the modified post-write data).

 (b) The responses to the requests _also_ may not be reordered. Even
     if the three requests have different serial numbers and an
     alert client could plausibly be able to deal with the responses
     arriving out of order, it is not permitted to send them that
     way.

Of course, if I submit a read request covering bytes 0-100, then
another covering bytes 50-150, there's nothing in theory to stop the
server from actually performing the reads in the opposite order, or
even doing a single read covering bytes 0-150 and returning two
substrings of it.

I don't see what's unclear about the wording as it is.
-- 
Simon Tatham         "Every person has a thinking part that wonders what
<anakin%pobox.com@localhost>    the part that isn't thinking isn't thinking about."