>> * Why does usb-serial set MAX_TRANFER to (PAGE_SIZE - 512)? What's the 
>> 512 for?
>>     
>
> A measure to make sure that a malicious user cannot use up unlimited
> amounts of kernel memory. 512 is the maximum packet size of ehci.
> Thus we make sure the number of packets on the page is an integer.
>   
I definitely understand limiting the number of outstanding URBs to avoid 
a DoS, but I don't follow why MAX_TRANSFER is being set to this 
particular value.   MAX_TRANSFER = PAGE_SIZE would seem like a better 
choice, as it wouldn't cause a PAGE_SIZE-sized write to fragment into 
two URBs (not that that's such a terrible thing anyway.) I'm not sure I 
see how the maximum packet size of the host enters into it.

Can you clarify?

-Ed


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