On Thu, 3 Oct 2002, Christopher R. Hertel wrote:

> 2) Is the MaxBufferSize in the NegProt Response a hard-and-fast rule
> (ignoring, of course, the MaxRawSize field and the depricated raw
> read/write SMBs)?

The smbfs source has some old comments about some servers not respecting
the max size (I'm guessing OS/2 ...). But AFAIK more modern servers follow
this.

I think the old internet-draft docs had a section about this being the
maximum allowed message size (you can probably find it in SNIA version
too).

> 3) In the SNIA doc, in section 4.1.1, in the explanation of the
> Capabilities bits, it says:
>
> CAP_LARGE_READX 0x4000 The server supports large SMB_COM_READ_ANDX
> (up to 64k)
> CAP_LARGE_WRITEX 0x8000 The server supports large SMB_COM_WRITE_ANDX
> (up to 64k)
>
> The "up to 64k" doesn't make sense. We can already fit 64k-1 bytes
> into the normal buffer without using LARGE_READX/WRITEX. What is the
> maximum, however? My guess is that the max would be MaxBufferSize.

I have understood this as: Even if you negotiate a smaller size than 64k
as the maximum message size, a LARGE_READX can still read 64k (or whatever
the max is).

A client may want to have a smaller maximum since it can then pre-allocate
smaller buffers (one page is a nice round number) for the not un-common
case of short requests/responses. But when reading file data it could be
useful to read a larger chunk in one go.

Btw, 64k is considered a large allocation inside the linux kernel, 128k
is/was the kmalloc maximum.

/Urban

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