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authorGustavo A. R. Silva <[email protected]>2022-08-31 14:12:42 -0500
committerDavid S. Miller <[email protected]>2022-09-03 09:51:10 +0100
commit5854a09b49574da5a77a0f36ad7b021a2661321d (patch)
treeec3173bf11696cd1db2c3866a5690844f72ab9b6 /tools/perf/scripts/python/bin/export-to-postgresql-report
parent2e5fb3223261366d1673c3827190c85a74b1aa56 (diff)
net/ipv4: Use __DECLARE_FLEX_ARRAY() helper
We now have a cleaner way to keep compatibility with user-space (a.k.a. not breaking it) when we need to keep in place a one-element array (for its use in user-space) together with a flexible-array member (for its use in kernel-space) without making it hard to read at the source level. This is through the use of the new __DECLARE_FLEX_ARRAY() helper macro. The size and memory layout of the structure is preserved after the changes. See below. Before changes: $ pahole -C ip_msfilter net/ipv4/igmp.o struct ip_msfilter { union { struct { __be32 imsf_multiaddr_aux; /* 0 4 */ __be32 imsf_interface_aux; /* 4 4 */ __u32 imsf_fmode_aux; /* 8 4 */ __u32 imsf_numsrc_aux; /* 12 4 */ __be32 imsf_slist[1]; /* 16 4 */ }; /* 0 20 */ struct { __be32 imsf_multiaddr; /* 0 4 */ __be32 imsf_interface; /* 4 4 */ __u32 imsf_fmode; /* 8 4 */ __u32 imsf_numsrc; /* 12 4 */ __be32 imsf_slist_flex[0]; /* 16 0 */ }; /* 0 16 */ }; /* 0 20 */ /* size: 20, cachelines: 1, members: 1 */ /* last cacheline: 20 bytes */ }; After changes: $ pahole -C ip_msfilter net/ipv4/igmp.o struct ip_msfilter { __be32 imsf_multiaddr; /* 0 4 */ __be32 imsf_interface; /* 4 4 */ __u32 imsf_fmode; /* 8 4 */ __u32 imsf_numsrc; /* 12 4 */ union { __be32 imsf_slist[1]; /* 16 4 */ struct { struct { } __empty_imsf_slist_flex; /* 16 0 */ __be32 imsf_slist_flex[0]; /* 16 0 */ }; /* 16 0 */ }; /* 16 4 */ /* size: 20, cachelines: 1, members: 5 */ /* last cacheline: 20 bytes */ }; In the past, we had to duplicate the whole original structure within a union, and update the names of all the members. Now, we just need to declare the flexible-array member to be used in kernel-space through the __DECLARE_FLEX_ARRAY() helper together with the one-element array, within a union. This makes the source code more clean and easier to read. Link: https://github.com/KSPP/linux/issues/193 Signed-off-by: Gustavo A. R. Silva <[email protected]> Reviewed-by: Kees Cook <[email protected]> Signed-off-by: David S. Miller <[email protected]>
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