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Message-ID: <bee16b72-f2e2-b113-9785-7f760be867df@huawei.com> Date: Thu, 25 Feb 2021 09:37:05 +0800 From: Chao Yu <yuchao0@...wei.com> To: "Gustavo A. R. Silva" <gustavoars@...nel.org>, Jaegeuk Kim <jaegeuk@...nel.org> CC: Chao Yu <chao@...nel.org>, <linux-hardening@...r.kernel.org>, <linux-kernel@...r.kernel.org>, <linux-f2fs-devel@...ts.sourceforge.net> Subject: Re: [f2fs-dev] [PATCH][next] f2fs: Replace one-element array with flexible-array member Hello, Gustavo, On 2021/2/25 3:03, Gustavo A. R. Silva 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]. I proposal to do the similar cleanup, and I've no objection on doing this. https://lore.kernel.org/patchwork/patch/869440/ Let's ask for Jaegeuk' opinion. > > Refactor the code according to the use of a flexible-array member in > struct f2fs_checkpoint, instead of a one-element arrays. > > Notice that a temporary pointer to void '*tmp_ptr' was used in order to > fix the following errors when using a flexible array instead of a one > element array in struct f2fs_checkpoint: > > CC [M] fs/f2fs/dir.o > In file included from fs/f2fs/dir.c:13: > fs/f2fs/f2fs.h: In function ‘__bitmap_ptr’: > fs/f2fs/f2fs.h:2227:40: error: invalid use of flexible array member > 2227 | return &ckpt->sit_nat_version_bitmap + offset + sizeof(__le32); > | ^ > fs/f2fs/f2fs.h:2227:49: error: invalid use of flexible array member > 2227 | return &ckpt->sit_nat_version_bitmap + offset + sizeof(__le32); > | ^ > fs/f2fs/f2fs.h:2238:40: error: invalid use of flexible array member > 2238 | return &ckpt->sit_nat_version_bitmap + offset; > | ^ > make[2]: *** [scripts/Makefile.build:287: fs/f2fs/dir.o] Error 1 > make[1]: *** [scripts/Makefile.build:530: fs/f2fs] Error 2 > make: *** [Makefile:1819: fs] Error 2 > > [1] https://en.wikipedia.org/wiki/Flexible_array_member > [2] https://www.kernel.org/doc/html/v5.9/process/deprecated.html#zero-length-and-one-element-arrays > > Link: https://github.com/KSPP/linux/issues/79 > Build-tested-by: kernel test robot <lkp@...el.com> > Link: https://lore.kernel.org/lkml/603647e4.DeEFbl4eqljuwAUe%25lkp@intel.com/ > Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org> > --- > fs/f2fs/f2fs.h | 5 +++-- > include/linux/f2fs_fs.h | 2 +- > 2 files changed, 4 insertions(+), 3 deletions(-) > > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h > index e2d302ae3a46..3f5cb097c30f 100644 > --- a/fs/f2fs/f2fs.h > +++ b/fs/f2fs/f2fs.h > @@ -2215,6 +2215,7 @@ static inline block_t __cp_payload(struct f2fs_sb_info *sbi) > static inline void *__bitmap_ptr(struct f2fs_sb_info *sbi, int flag) > { > struct f2fs_checkpoint *ckpt = F2FS_CKPT(sbi); > + void *tmp_ptr = &ckpt->sit_nat_version_bitmap; > int offset; > > if (is_set_ckpt_flags(sbi, CP_LARGE_NAT_BITMAP_FLAG)) { > @@ -2224,7 +2225,7 @@ static inline void *__bitmap_ptr(struct f2fs_sb_info *sbi, int flag) > * if large_nat_bitmap feature is enabled, leave checksum > * protection for all nat/sit bitmaps. > */ > - return &ckpt->sit_nat_version_bitmap + offset + sizeof(__le32); > + return tmp_ptr + offset + sizeof(__le32); > } > > if (__cp_payload(sbi) > 0) { > @@ -2235,7 +2236,7 @@ static inline void *__bitmap_ptr(struct f2fs_sb_info *sbi, int flag) > } else { > offset = (flag == NAT_BITMAP) ? > le32_to_cpu(ckpt->sit_ver_bitmap_bytesize) : 0; > - return &ckpt->sit_nat_version_bitmap + offset; > + return tmp_ptr + offset; > } > } > > diff --git a/include/linux/f2fs_fs.h b/include/linux/f2fs_fs.h > index c6cc0a566ef5..5487a80617a3 100644 > --- a/include/linux/f2fs_fs.h > +++ b/include/linux/f2fs_fs.h > @@ -168,7 +168,7 @@ struct f2fs_checkpoint { > unsigned char alloc_type[MAX_ACTIVE_LOGS]; > > /* SIT and NAT version bitmap */ > - unsigned char sit_nat_version_bitmap[1]; > + unsigned char sit_nat_version_bitmap[]; > } __packed; > > #define CP_CHKSUM_OFFSET 4092 /* default chksum offset in checkpoint */ >
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