| Message ID | 20210323224858.GA293698@embeddedor (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [next] UAPI: nfsfh.h: Replace one-element array with flexible-array member | expand |
On 3/25/21 08:45, David Laight wrote: > From: Gustavo A. R. Silva >> Sent: 23 March 2021 22:49 >> >> 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 */ >> }; > > Could you use the simpler: >> struct nfs_fhbase_new { >> __u8 fb_version; >> __u8 fb_auth_type; >> __u8 fb_fsid_type; >> __u8 fb_fileid_type; >> union { >> __u32 fb_auth[1]; >> __u32 fb_auth_flex[0]; >> }; >> }; > > Although I'm not certain flexible arrays are supported > as the last element of a union. Nope; this is not allowed: https://godbolt.org/z/14vd4o8na -- Gustavo
From: Gustavo A. R. Silva > Sent: 23 March 2021 22:49 > > 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 */ > }; Could you use the simpler: > struct nfs_fhbase_new { > __u8 fb_version; > __u8 fb_auth_type; > __u8 fb_fsid_type; > __u8 fb_fileid_type; > union { > __u32 fb_auth[1]; > __u32 fb_auth_flex[0]; > }; > }; Although I'm not certain flexible arrays are supported as the last element of a union. You might need to use a named anonymous structure for the four __u8 fields and create two different structures that include the extra field on the end. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
From: Gustavo A. R. Silva > Sent: 25 March 2021 13:18 > > On 3/25/21 08:45, David Laight wrote: > > From: Gustavo A. R. Silva > >> Sent: 23 March 2021 22:49 > >> > >> 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 */ > >> }; > > > > Could you use the simpler: > >> struct nfs_fhbase_new { > >> __u8 fb_version; > >> __u8 fb_auth_type; > >> __u8 fb_fsid_type; > >> __u8 fb_fileid_type; > >> union { > >> __u32 fb_auth[1]; > >> __u32 fb_auth_flex[0]; > >> }; > >> }; > > > > Although I'm not certain flexible arrays are supported > > as the last element of a union. > > Nope; this is not allowed: https://godbolt.org/z/14vd4o8na Nothing an extra 'struct {__u32 fb_auth_flex[0]; }'; won't solve. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
On 3/25/21 10:29, David Laight wrote: >>> >>> Could you use the simpler: >>>> struct nfs_fhbase_new { >>>> __u8 fb_version; >>>> __u8 fb_auth_type; >>>> __u8 fb_fsid_type; >>>> __u8 fb_fileid_type; >>>> union { >>>> __u32 fb_auth[1]; >>>> __u32 fb_auth_flex[0]; >>>> }; >>>> }; >>> >>> Although I'm not certain flexible arrays are supported >>> as the last element of a union. >> >> Nope; this is not allowed: https://godbolt.org/z/14vd4o8na > > Nothing an extra 'struct {__u32 fb_auth_flex[0]; }'; won't solve. We don't want to introduce zero-length arrays [1]. -- Gustavo [1] https://www.kernel.org/doc/html/v5.10/process/deprecated.html#zero-length-and-one-element-arrays
From: Gustavo A. R. Silva > Sent: 25 March 2021 21:12 > > On 3/25/21 10:29, David Laight wrote: > > >>> > >>> Could you use the simpler: > >>>> struct nfs_fhbase_new { > >>>> __u8 fb_version; > >>>> __u8 fb_auth_type; > >>>> __u8 fb_fsid_type; > >>>> __u8 fb_fileid_type; > >>>> union { > >>>> __u32 fb_auth[1]; > >>>> __u32 fb_auth_flex[0]; > >>>> }; > >>>> }; > >>> > >>> Although I'm not certain flexible arrays are supported > >>> as the last element of a union. > >> > >> Nope; this is not allowed: https://godbolt.org/z/14vd4o8na > > > > Nothing an extra 'struct {__u32 fb_auth_flex[0]; }'; won't solve. > > We don't want to introduce zero-length arrays [1]. I probably meant to write [] not [0] - doesn't affect the idea. The real problem is that the compiler is likely to start rejecting references to a flex array that go beyond the end of the outer structure. Thinking back, isn't fb_auth[] at least one entry long? So it could be: struct nfs_fhbase_new { __u8 fb_version; __u8 fb_auth_type; __u8 fb_fsid_type; __u8 fb_fileid_type; __u32 fb_auth[1]; __u32 fb_auth_extra[]; }; (I've missed the 0 out this time...) David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
On 3/26/21 03:17, David Laight wrote: > From: Gustavo A. R. Silva >> Sent: 25 March 2021 21:12 >> >> On 3/25/21 10:29, David Laight wrote: >> >>>>> >>>>> Could you use the simpler: >>>>>> struct nfs_fhbase_new { >>>>>> __u8 fb_version; >>>>>> __u8 fb_auth_type; >>>>>> __u8 fb_fsid_type; >>>>>> __u8 fb_fileid_type; >>>>>> union { >>>>>> __u32 fb_auth[1]; >>>>>> __u32 fb_auth_flex[0]; >>>>>> }; >>>>>> }; >>>>> >>>>> Although I'm not certain flexible arrays are supported >>>>> as the last element of a union. >>>> >>>> Nope; this is not allowed: https://godbolt.org/z/14vd4o8na >>> >>> Nothing an extra 'struct {__u32 fb_auth_flex[0]; }'; won't solve. >> >> We don't want to introduce zero-length arrays [1]. > > I probably meant to write [] not [0] - doesn't affect the idea. > > The real problem is that the compiler is likely to start rejecting > references to a flex array that go beyond the end of the outer > structure. > > Thinking back, isn't fb_auth[] at least one entry long? > So it could be: > > struct nfs_fhbase_new { > __u8 fb_version; > __u8 fb_auth_type; > __u8 fb_fsid_type; > __u8 fb_fileid_type; > __u32 fb_auth[1]; > __u32 fb_auth_extra[]; > }; I don't think this is a great idea because, contrary to the change I'm proposing, in this case memory regions for fb_auth and fb_auth_extra don't actually overlap. -- Gustavo
On 3/29/21 09:57, Chuck Lever wrote: > Sorry for the reply via gmail, the original patch did not show up in > my Oracle mailbox. > > I've been waiting for a resolution of this thread (and perhaps a > Reviewed-by). But in > the meantime I've committed this, provisionally, to the for-next topic branch in > > git://git.kernel.org/pub/scm/linux/kernel/git/cel/linux.git Awesome. :) Thanks, Chuck. -- Gustavo > On Wed, Mar 24, 2021 at 4:39 AM Gustavo A. R. Silva > <gustavoars@kernel.org> wrote: >> >> 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> >> --- >> include/uapi/linux/nfsd/nfsfh.h | 27 +++++++++++++++++++-------- >> 1 file changed, 19 insertions(+), 8 deletions(-) >> >> diff --git a/include/uapi/linux/nfsd/nfsfh.h b/include/uapi/linux/nfsd/nfsfh.h >> index ff0ca88b1c8f..427294dd56a1 100644 >> --- a/include/uapi/linux/nfsd/nfsfh.h >> +++ b/include/uapi/linux/nfsd/nfsfh.h >> @@ -64,13 +64,24 @@ struct nfs_fhbase_old { >> * in include/linux/exportfs.h for currently registered values. >> */ >> struct nfs_fhbase_new { >> - __u8 fb_version; /* == 1, even => nfs_fhbase_old */ >> - __u8 fb_auth_type; >> - __u8 fb_fsid_type; >> - __u8 fb_fileid_type; >> - __u32 fb_auth[1]; >> -/* __u32 fb_fsid[0]; floating */ >> -/* __u32 fb_fileid[0]; floating */ >> + union { >> + struct { >> + __u8 fb_version_aux; /* == 1, even => nfs_fhbase_old */ >> + __u8 fb_auth_type_aux; >> + __u8 fb_fsid_type_aux; >> + __u8 fb_fileid_type_aux; >> + __u32 fb_auth[1]; >> + /* __u32 fb_fsid[0]; floating */ >> + /* __u32 fb_fileid[0]; floating */ >> + }; >> + struct { >> + __u8 fb_version; /* == 1, even => nfs_fhbase_old */ >> + __u8 fb_auth_type; >> + __u8 fb_fsid_type; >> + __u8 fb_fileid_type; >> + __u32 fb_auth_flex[]; /* flexible-array member */ >> + }; >> + }; >> }; >> >> struct knfsd_fh { >> @@ -97,7 +108,7 @@ struct knfsd_fh { >> #define fh_fsid_type fh_base.fh_new.fb_fsid_type >> #define fh_auth_type fh_base.fh_new.fb_auth_type >> #define fh_fileid_type fh_base.fh_new.fb_fileid_type >> -#define fh_fsid fh_base.fh_new.fb_auth >> +#define fh_fsid fh_base.fh_new.fb_auth_flex >> >> /* Do not use, provided for userspace compatiblity. */ >> #define fh_auth fh_base.fh_new.fb_auth >> -- >> 2.27.0 >> > >
Sorry for the reply via gmail, the original patch did not show up in my Oracle mailbox. I've been waiting for a resolution of this thread (and perhaps a Reviewed-by). But in the meantime I've committed this, provisionally, to the for-next topic branch in git://git.kernel.org/pub/scm/linux/kernel/git/cel/linux.git On Wed, Mar 24, 2021 at 4:39 AM Gustavo A. R. Silva <gustavoars@kernel.org> wrote: > > 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> > --- > include/uapi/linux/nfsd/nfsfh.h | 27 +++++++++++++++++++-------- > 1 file changed, 19 insertions(+), 8 deletions(-) > > diff --git a/include/uapi/linux/nfsd/nfsfh.h b/include/uapi/linux/nfsd/nfsfh.h > index ff0ca88b1c8f..427294dd56a1 100644 > --- a/include/uapi/linux/nfsd/nfsfh.h > +++ b/include/uapi/linux/nfsd/nfsfh.h > @@ -64,13 +64,24 @@ struct nfs_fhbase_old { > * in include/linux/exportfs.h for currently registered values. > */ > struct nfs_fhbase_new { > - __u8 fb_version; /* == 1, even => nfs_fhbase_old */ > - __u8 fb_auth_type; > - __u8 fb_fsid_type; > - __u8 fb_fileid_type; > - __u32 fb_auth[1]; > -/* __u32 fb_fsid[0]; floating */ > -/* __u32 fb_fileid[0]; floating */ > + union { > + struct { > + __u8 fb_version_aux; /* == 1, even => nfs_fhbase_old */ > + __u8 fb_auth_type_aux; > + __u8 fb_fsid_type_aux; > + __u8 fb_fileid_type_aux; > + __u32 fb_auth[1]; > + /* __u32 fb_fsid[0]; floating */ > + /* __u32 fb_fileid[0]; floating */ > + }; > + struct { > + __u8 fb_version; /* == 1, even => nfs_fhbase_old */ > + __u8 fb_auth_type; > + __u8 fb_fsid_type; > + __u8 fb_fileid_type; > + __u32 fb_auth_flex[]; /* flexible-array member */ > + }; > + }; > }; > > struct knfsd_fh { > @@ -97,7 +108,7 @@ struct knfsd_fh { > #define fh_fsid_type fh_base.fh_new.fb_fsid_type > #define fh_auth_type fh_base.fh_new.fb_auth_type > #define fh_fileid_type fh_base.fh_new.fb_fileid_type > -#define fh_fsid fh_base.fh_new.fb_auth > +#define fh_fsid fh_base.fh_new.fb_auth_flex > > /* Do not use, provided for userspace compatiblity. */ > #define fh_auth fh_base.fh_new.fb_auth > -- > 2.27.0 >
diff --git a/include/uapi/linux/nfsd/nfsfh.h b/include/uapi/linux/nfsd/nfsfh.h index ff0ca88b1c8f..427294dd56a1 100644 --- a/include/uapi/linux/nfsd/nfsfh.h +++ b/include/uapi/linux/nfsd/nfsfh.h @@ -64,13 +64,24 @@ struct nfs_fhbase_old { * in include/linux/exportfs.h for currently registered values. */ struct nfs_fhbase_new { - __u8 fb_version; /* == 1, even => nfs_fhbase_old */ - __u8 fb_auth_type; - __u8 fb_fsid_type; - __u8 fb_fileid_type; - __u32 fb_auth[1]; -/* __u32 fb_fsid[0]; floating */ -/* __u32 fb_fileid[0]; floating */ + union { + struct { + __u8 fb_version_aux; /* == 1, even => nfs_fhbase_old */ + __u8 fb_auth_type_aux; + __u8 fb_fsid_type_aux; + __u8 fb_fileid_type_aux; + __u32 fb_auth[1]; + /* __u32 fb_fsid[0]; floating */ + /* __u32 fb_fileid[0]; floating */ + }; + struct { + __u8 fb_version; /* == 1, even => nfs_fhbase_old */ + __u8 fb_auth_type; + __u8 fb_fsid_type; + __u8 fb_fileid_type; + __u32 fb_auth_flex[]; /* flexible-array member */ + }; + }; }; struct knfsd_fh { @@ -97,7 +108,7 @@ struct knfsd_fh { #define fh_fsid_type fh_base.fh_new.fb_fsid_type #define fh_auth_type fh_base.fh_new.fb_auth_type #define fh_fileid_type fh_base.fh_new.fb_fileid_type -#define fh_fsid fh_base.fh_new.fb_auth +#define fh_fsid fh_base.fh_new.fb_auth_flex /* Do not use, provided for userspace compatiblity. */ #define fh_auth fh_base.fh_new.fb_auth
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> --- include/uapi/linux/nfsd/nfsfh.h | 27 +++++++++++++++++++-------- 1 file changed, 19 insertions(+), 8 deletions(-)