How to allocate pages for a scatter-gather buffer?

[Alan Stern]

Jens:

Thanks for your help in tracking down that problem with the usb-storage 
sddr09 driver.

Now a slightly different question.  Suppose I want to allocate some pages
as a scatter-gather buffer for I/O to a device.  I've got the device's
dma_mask; what's the right way to convert that to a GFP bitmask for
alloc_pages() or get_free_pages()?

Also, assuming I'll have to use memcpy() to transfer data into or out of 
the scatter-gather buffer (so it will have to get a kernel virtual mapping 
at some point), am I better off using alloc_pages() followed by 
kmap_atomic()/kunmap_atomic() or get_free_pages()?  Or even kmalloc()?

Alan Stern

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