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UAPI: nfsfh.h: Replace one-element array with flexible-array member
There is a regular need in the kernel to provide a way to declare having a dynamically sized set of trailing elements in a structure. Kernel code should always use “flexible array members”[1] for these cases. The older style of one-element or zero-length arrays should no longer be used[2]. Use an anonymous union with a couple of anonymous structs in order to keep userspace unchanged: $ pahole -C nfs_fhbase_new fs/nfsd/nfsfh.o struct nfs_fhbase_new { union { struct { __u8 fb_version_aux; /* 0 1 */ __u8 fb_auth_type_aux; /* 1 1 */ __u8 fb_fsid_type_aux; /* 2 1 */ __u8 fb_fileid_type_aux; /* 3 1 */ __u32 fb_auth[1]; /* 4 4 */ }; /* 0 8 */ struct { __u8 fb_version; /* 0 1 */ __u8 fb_auth_type; /* 1 1 */ __u8 fb_fsid_type; /* 2 1 */ __u8 fb_fileid_type; /* 3 1 */ __u32 fb_auth_flex[0]; /* 4 0 */ }; /* 0 4 */ }; /* 0 8 */ /* size: 8, cachelines: 1, members: 1 */ /* last cacheline: 8 bytes */ }; Also, this helps with the ongoing efforts to enable -Warray-bounds by fixing the following warnings: fs/nfsd/nfsfh.c: In function ‘nfsd_set_fh_dentry’: fs/nfsd/nfsfh.c:191:41: warning: array subscript 1 is above array bounds of ‘__u32[1]’ {aka ‘unsigned int[1]’} [-Warray-bounds] 191 | ntohl((__force __be32)fh->fh_fsid[1]))); | ~~~~~~~~~~~^~~ ./include/linux/kdev_t.h:12:46: note: in definition of macro ‘MKDEV’ 12 | #define MKDEV(ma,mi) (((ma) << MINORBITS) | (mi)) | ^~ ./include/uapi/linux/byteorder/little_endian.h:40:26: note: in expansion of macro ‘__swab32’ 40 | #define __be32_to_cpu(x) __swab32((__force __u32)(__be32)(x)) | ^~~~~~~~ ./include/linux/byteorder/generic.h:136:21: note: in expansion of macro ‘__be32_to_cpu’ 136 | #define ___ntohl(x) __be32_to_cpu(x) | ^~~~~~~~~~~~~ ./include/linux/byteorder/generic.h:140:18: note: in expansion of macro ‘___ntohl’ 140 | #define ntohl(x) ___ntohl(x) | ^~~~~~~~ fs/nfsd/nfsfh.c:191:8: note: in expansion of macro ‘ntohl’ 191 | ntohl((__force __be32)fh->fh_fsid[1]))); | ^~~~~ fs/nfsd/nfsfh.c:192:32: warning: array subscript 2 is above array bounds of ‘__u32[1]’ {aka ‘unsigned int[1]’} [-Warray-bounds] 192 | fh->fh_fsid[1] = fh->fh_fsid[2]; | ~~~~~~~~~~~^~~ fs/nfsd/nfsfh.c:192:15: warning: array subscript 1 is above array bounds of ‘__u32[1]’ {aka ‘unsigned int[1]’} [-Warray-bounds] 192 | fh->fh_fsid[1] = fh->fh_fsid[2]; | ~~~~~~~~~~~^~~ [1] https://en.wikipedia.org/wiki/Flexible_array_member [2] https://www.kernel.org/doc/html/v5.10/process/deprecated.html#zero-length-and-one-element-arrays Link: https://github.com/KSPP/linux/issues/79 Link: https://github.com/KSPP/linux/issues/109 Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
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1 changed files with 19 additions and 8 deletions
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@ -64,13 +64,24 @@ struct nfs_fhbase_old {
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* in include/linux/exportfs.h for currently registered values.
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*/
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struct nfs_fhbase_new {
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__u8 fb_version; /* == 1, even => nfs_fhbase_old */
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__u8 fb_auth_type;
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__u8 fb_fsid_type;
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__u8 fb_fileid_type;
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__u32 fb_auth[1];
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/* __u32 fb_fsid[0]; floating */
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/* __u32 fb_fileid[0]; floating */
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union {
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struct {
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__u8 fb_version_aux; /* == 1, even => nfs_fhbase_old */
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__u8 fb_auth_type_aux;
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__u8 fb_fsid_type_aux;
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__u8 fb_fileid_type_aux;
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__u32 fb_auth[1];
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/* __u32 fb_fsid[0]; floating */
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/* __u32 fb_fileid[0]; floating */
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};
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struct {
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__u8 fb_version; /* == 1, even => nfs_fhbase_old */
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__u8 fb_auth_type;
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__u8 fb_fsid_type;
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__u8 fb_fileid_type;
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__u32 fb_auth_flex[]; /* flexible-array member */
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};
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};
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};
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struct knfsd_fh {
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@ -97,7 +108,7 @@ struct knfsd_fh {
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#define fh_fsid_type fh_base.fh_new.fb_fsid_type
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#define fh_auth_type fh_base.fh_new.fb_auth_type
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#define fh_fileid_type fh_base.fh_new.fb_fileid_type
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#define fh_fsid fh_base.fh_new.fb_auth
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#define fh_fsid fh_base.fh_new.fb_auth_flex
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/* Do not use, provided for userspace compatiblity. */
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#define fh_auth fh_base.fh_new.fb_auth
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