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e9be933959
The crypto/krb5 library accepts data in scatterlist form, but
the GSS-API layer presents RPC payloads as struct xdr_buf.
Bridge that gap with a pair of helper functions:
xdr_buf_to_sg() - populate a caller-supplied scatterlist
array from a byte range
xdr_buf_to_sg_alloc() - populate a caller-supplied inline
scatterlist, chaining to a heap-
allocated overflow for large payloads
The inline array (typically stack-allocated at eight entries)
covers the common case of small RPCs with no heap allocation
on the encrypt/decrypt path. Only buffers spanning many pages
incur a kmalloc for the chained extension.
The segment-walking logic follows the same head, page array,
tail traversal as xdr_process_buf(), but populates a
scatterlist directly rather than invoking a per-segment
callback. sg_next() traversal makes the walker safe for
chained scatterlists. Once subsequent patches reroute all
per-message crypto operations through crypto/krb5,
xdr_process_buf() loses its last callers and is removed.
Assisted-by: Claude:claude-opus-4-6
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Acked-by: Anna Schumaker <anna.schumaker@hammerspace.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>