Re: [Xen-devel] [PATCH v5 10/12] livepatch: Handle arbitrary size names with the list operation

[Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>]

On 11/14/19 1:06 PM, Pawel Wieczorkiewicz wrote:
> The payloads' name strings can be of arbitrary size (typically small
> with an upper bound of XEN_LIVEPATCH_NAME_SIZE).
> Current implementation of the list operation interface allows to copy
> names in the XEN_LIVEPATCH_NAME_SIZE chunks regardless of its actual
> size and enforces space allocation requirements on userland tools.
> 
> To unify and simplify the interface, handle the name strings of
> arbitrary size by copying them in adhering chunks to the userland.
> In order to let the userland allocate enough space for the incoming
> data add an auxiliary interface xc_livepatch_list_get_sizes() that
> provides the current number of payload entries and the total size of
> all name strings. This is achieved by extending the sysctl list
> interface with an extra fields: name_total_size.
> 
> The xc_livepatch_list_get_sizes() issues the livepatch sysctl list
> operation with the nr field set to 0. In this mode the operation
> returns the number of payload entries and calculates the total sizes
> for all payloads' names.
> When the sysctl operation is issued with a non-zero nr field (for
> instance with a value obtained earlier with the prior call to the
> xc_livepatch_list_get_sizes()) the new field name_total_size provides
> the total size of actually copied data.
> 
> Extend the libxc to handle the name back-to-back data transfers.
> 
> The xen-livepatch tool is modified to start the list operation with a
> call to the xc_livepatch_list_get_sizes() to obtain the actual number
> of payloads as well as the necessary space for names.
> The tool now always requests the actual number of entries and leaves
> the preemption handling to the libxc routine. The libxc still returns
> 'done' and 'left' parameters with the same semantic allowing the tool
> to detect anomalies and react to them. At the moment it is expected
> that the tool receives the exact number of entries as requested.
> The xen-livepatch tool has been also modified to handle the name
> back-to-back transfers correctly.
> 
> Signed-off-by: Pawel Wieczorkiewicz <wipawel@xxxxxxxxx>
> Reviewed-by: Andra-Irina Paraschiv <andraprs@xxxxxxxxxx>
> Reviewed-by: Bjoern Doebel <doebel@xxxxxxxxx>
> Reviewed-by: Martin Pohlack <mpohlack@xxxxxxxxx>
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> ---
Reviewed-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>

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