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    Subject[PATCH] UAPI linux/fs.h: add a warning about wrong ioctl argument types
    FS_IOC_SETVERSION ioctls are declared for historical reasons with a long
    argument, while in practice they take an int argument. This is
    unfortunately not possible to fix that without breaking the kernel ABI.

    However good programmers actually lookup for the argument type of these
    ioctls in <fs/linux.h> and end-up using a long. This breaks on 64-bit
    big endian machines.

    Instead of letting the same "mistake" to be done again and again, add an
    explanation to <fs/linux.h> so that people use the correct argument type
    in their code. Also add a small comment on the same line while staying
    within 80 characters so that the issue appears when doing a grep on this

    Cc: Alexander Viro <>
    Cc: Christoph Hellwig <>
    Cc: Theodore Ts'o <>
    Signed-off-by: Aurelien Jarno <>
    include/uapi/linux/fs.h | 14 ++++++++++----
    1 file changed, 10 insertions(+), 4 deletions(-)

    diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
    index 6c28b61..baeb803 100644
    --- a/include/uapi/linux/fs.h
    +++ b/include/uapi/linux/fs.h
    @@ -154,10 +154,16 @@ struct inodes_stat_t {
    #define FITHAW _IOWR('X', 120, int) /* Thaw */
    #define FITRIM _IOWR('X', 121, struct fstrim_range) /* Trim */

    -#define FS_IOC_GETFLAGS _IOR('f', 1, long)
    -#define FS_IOC_SETFLAGS _IOW('f', 2, long)
    -#define FS_IOC_GETVERSION _IOR('v', 1, long)
    -#define FS_IOC_SETVERSION _IOW('v', 2, long)
    + * WARNING: The next four following ioctls actually take an int argument
    + * despite their definition. This is important to support 64-bit big-endian
    + * machines.
    + */
    +#define FS_IOC_GETFLAGS _IOR('f', 1, long) /* should be int */
    +#define FS_IOC_SETFLAGS _IOW('f', 2, long) /* should be int */
    +#define FS_IOC_GETVERSION _IOR('v', 1, long) /* should be int */
    +#define FS_IOC_SETVERSION _IOW('v', 2, long) /* should be int */
    #define FS_IOC_FIEMAP _IOWR('f', 11, struct fiemap)
    #define FS_IOC32_GETFLAGS _IOR('f', 1, int)
    #define FS_IOC32_SETFLAGS _IOW('f', 2, int)

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      Last update: 2013-11-27 12:01    [W:0.024 / U:2.556 seconds]
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