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lib_xsk_extend: Add comment describing XDP metadata and BTF

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Add a large comments to the most central piece of code that
access the right offset into the metadata based on the BTF
info we have extracted.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
This commit is contained in:
Jesper Dangaard Brouer
2021-11-05 10:13:42 +01:00
parent f46743a75f
commit b028f24513
1 changed files with 5 additions and 0 deletions
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5
AF_XDP-interaction/lib_xsk_extend.c
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@@ -180,6 +180,11 @@ int xsk_btf__read_member(void **dest, size_t size,
if (entry->size != size) if (entry->size != size)
return -EFAULT; return -EFAULT;
/* Remember XDP-hints are located in metadata (xdp_ctx->data_meta),
* which is located just before packet data starts. Thus, accessing BTF
* described memory area via a negative offset, based on the size of the
* BTF struct that XDP-prog used.
*/
*dest = (void *)((char *)addr - xbi->type->size + entry->offset); *dest = (void *)((char *)addr - xbi->type->size + entry->offset);
return 0; return 0;
} }