On Thu, Jul 19, 2018 at 08:52:32AM -0700, Tadeusz Struk wrote:

Currently to read a response from the TPM device an application needs
provide "big enough" buffer for the whole response and read it in one go.
The application doesn't know how big the response it beforehand so it
always needs to maintain a 4K buffer and read the max (4K).
In case if the user of the TSS library doesn't provide big enough buffer
the TCTI spec says that the library should set the required size and return
TSS2_TCTI_RC_INSUFFICIENT_BUFFER error code so that the application could
allocate a bigger buffer and call receive again.
To make it possible in the TSS library this requires being able to do
partial reads from the driver.
The library would read the header first to get the actual size of the
response from the header and then read the rest of the response.
This patch adds support for partial reads.

You should solve this in user space, the kernel API requires a full
sized buffer here, the tss library should always provide such an
internal buffer and then implement whatever scheme TSS wants by
memcpying from that buffer..

Jason
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