Re: [RFC][PATCH v2 04/10] ext2: use common file type conversion

[Amir Goldstein]

On Tue, Oct 23, 2018 at 11:19 PM Phillip Potter <phil@xxxxxxxxxxxxxxxx> wrote:
>
> Deduplicate the ext2 file type conversion implementation.
>
> Original patch by Amir Goldstein.
>
> v2:
> - Rebased against Linux 4.19 by Phillip Potter
> - This version does not remove EXT2_FT_x enum from fs/ext2/ext2.h,
>   as these values are now used in compile-time checks added by
>   Phillip Potter to make sure they remain the same as FT_x values
>
> v1:
> - Initial implementation
>

Same comments as how to apply a patch and about changelog as patch 1.
Won't repeat for other patches.

I think it would be also good to mention there is a lurking bug if code
ever tries to access ext2_type_by_mode[S_IFMT] because on-disk
data is corrupted.

> Signed-off-by: Phillip Potter <phil@xxxxxxxxxxxxxxxx>
> ---
>  fs/ext2/dir.c | 51 ++++++++++++++++++++++-----------------------------
>  1 file changed, 22 insertions(+), 29 deletions(-)
>
> diff --git a/fs/ext2/dir.c b/fs/ext2/dir.c
> index 3b8114def693..420d4b9e8980 100644
> --- a/fs/ext2/dir.c
> +++ b/fs/ext2/dir.c
> @@ -252,33 +252,10 @@ ext2_validate_entry(char *base, unsigned offset, unsigned mask)
>         return (char *)p - base;
>  }
>
> -static unsigned char ext2_filetype_table[EXT2_FT_MAX] = {
> -       [EXT2_FT_UNKNOWN]       = DT_UNKNOWN,
> -       [EXT2_FT_REG_FILE]      = DT_REG,
> -       [EXT2_FT_DIR]           = DT_DIR,
> -       [EXT2_FT_CHRDEV]        = DT_CHR,
> -       [EXT2_FT_BLKDEV]        = DT_BLK,
> -       [EXT2_FT_FIFO]          = DT_FIFO,
> -       [EXT2_FT_SOCK]          = DT_SOCK,
> -       [EXT2_FT_SYMLINK]       = DT_LNK,
> -};
> -
> -#define S_SHIFT 12
> -static unsigned char ext2_type_by_mode[S_IFMT >> S_SHIFT] = {
> -       [S_IFREG >> S_SHIFT]    = EXT2_FT_REG_FILE,
> -       [S_IFDIR >> S_SHIFT]    = EXT2_FT_DIR,
> -       [S_IFCHR >> S_SHIFT]    = EXT2_FT_CHRDEV,
> -       [S_IFBLK >> S_SHIFT]    = EXT2_FT_BLKDEV,
> -       [S_IFIFO >> S_SHIFT]    = EXT2_FT_FIFO,
> -       [S_IFSOCK >> S_SHIFT]   = EXT2_FT_SOCK,
> -       [S_IFLNK >> S_SHIFT]    = EXT2_FT_SYMLINK,
> -};
> -
>  static inline void ext2_set_de_type(ext2_dirent *de, struct inode *inode)
>  {
> -       umode_t mode = inode->i_mode;
>         if (EXT2_HAS_INCOMPAT_FEATURE(inode->i_sb, EXT2_FEATURE_INCOMPAT_FILETYPE))
> -               de->file_type = ext2_type_by_mode[(mode & S_IFMT)>>S_SHIFT];
> +               de->file_type = fs_umode_to_ftype(inode->i_mode);
>         else
>                 de->file_type = 0;
>  }
> @@ -293,14 +270,14 @@ ext2_readdir(struct file *file, struct dir_context *ctx)
>         unsigned long n = pos >> PAGE_SHIFT;
>         unsigned long npages = dir_pages(inode);
>         unsigned chunk_mask = ~(ext2_chunk_size(inode)-1);
> -       unsigned char *types = NULL;
>         bool need_revalidate = !inode_eq_iversion(inode, file->f_version);
> +       bool has_filetype;
>
>         if (pos > inode->i_size - EXT2_DIR_REC_LEN(1))
>                 return 0;
>
> -       if (EXT2_HAS_INCOMPAT_FEATURE(sb, EXT2_FEATURE_INCOMPAT_FILETYPE))
> -               types = ext2_filetype_table;
> +       has_filetype =
> +               EXT2_HAS_INCOMPAT_FEATURE(sb, EXT2_FEATURE_INCOMPAT_FILETYPE);
>
>         for ( ; n < npages; n++, offset = 0) {
>                 char *kaddr, *limit;
> @@ -335,8 +312,24 @@ ext2_readdir(struct file *file, struct dir_context *ctx)
>                         if (de->inode) {
>                                 unsigned char d_type = DT_UNKNOWN;
>
> -                               if (types && de->file_type < EXT2_FT_MAX)
> -                                       d_type = types[de->file_type];
> +                               /*
> +                                * compile-time asserts that generic FT_x types
> +                                * still match EXT2_FT_x types - no need to list
> +                                * for other functions as well as build will
> +                                * fail either way
> +                                */
> +                               BUILD_BUG_ON(EXT2_FT_UNKNOWN != FT_UNKNOWN);
> +                               BUILD_BUG_ON(EXT2_FT_REG_FILE != FT_REG_FILE);
> +                               BUILD_BUG_ON(EXT2_FT_DIR != FT_DIR);
> +                               BUILD_BUG_ON(EXT2_FT_CHRDEV != FT_CHRDEV);
> +                               BUILD_BUG_ON(EXT2_FT_BLKDEV != FT_BLKDEV);
> +                               BUILD_BUG_ON(EXT2_FT_FIFO != FT_FIFO);
> +                               BUILD_BUG_ON(EXT2_FT_SOCK != FT_SOCK);
> +                               BUILD_BUG_ON(EXT2_FT_SYMLINK != FT_SYMLINK);
> +                               BUILD_BUG_ON(EXT2_FT_MAX != FT_MAX);

This bunch would look much nicer in ext2_set_de_type().
Always try to put those build time asserts near relevant code
but also at the "beginning of something" in a place more pleasant
to the eye.

> +
> +                               if (has_filetype)
> +                                       d_type = fs_dtype(de->file_type);
>
>                                 if (!dir_emit(ctx, de->name, de->name_len,
>                                                 le32_to_cpu(de->inode),
> --
> 2.17.2
>