On Sat, Jun 17, 2017 at 01:59:48PM -0600, Jens Axboe wrote:
> We have a pwritev2(2) interface based on passing in flags. Add an
> fcntl interface for querying these flags, and also for setting them
> as well:
>
> F_GET_RW_HINT Returns the read/write hint set. Right now it
> will be one of the WRITE_LIFE_* values.
>
> F_SET_RW_HINT Pass in rw_hint type to set the read/write hint.
> Only WRITE_LIFE_* hints are currently supported.
> Returns 0 on succes, -1 otherwise.
>
> Sample program testing/implementing basic setting/getting of write
> hints is below.
>
> /*
> * writehint.c: check or set a file/inode write hint
> */
>
> static char *str[] = { "WRITE_LIFE_NONE", "WRITE_LIFE_SHORT",
> "WRITE_LIFE_MEDIUM", "WRITE_LIFE_LONG",
> "WRITE_LIFE_EXTREME" };
>
> int main(int argc, char *argv[])
> {
> int hint = -1, fd, ret;
>
> if (argc < 2) {
> fprintf(stderr, "%s: dev <hint>\n", argv[0]);
> return 1;
> }
>
> fd = open(argv[1], O_RDONLY);
> if (fd < 0) {
> perror("open");
> return 2;
> }
>
> if (argc > 2)
> hint = atoi(argv[2]);
>
> if (hint == -1) {
> ret = fcntl(fd, F_GET_RW_HINT);
> if (ret < 0) {
> perror("fcntl: F_GET_RW_HINT");
> return 3;
> }
> hint = ret;
> } else {
> ret = fcntl(fd, F_SET_RW_HINT, hint);
> if (ret < 0) {
> perror("fcntl: F_SET_RW_HINT");
> return 4;
> }
> }
>
> printf("%s: %shint %s\n", argv[1], hint != -1 ? "set " : "", str[hint]);
> close(fd);
> return 0;
> }
>
> Signed-off-by: Jens Axboe <ax...@kernel.dk>
> ---
> fs/fcntl.c | 38 ++++++++++++++++++++++++++++++++++++++
> include/uapi/linux/fcntl.h | 6 ++++++
> 2 files changed, 44 insertions(+)
>
> diff --git a/fs/fcntl.c b/fs/fcntl.c
> index f4e7267d117f..417ce336c875 100644
> --- a/fs/fcntl.c
> +++ b/fs/fcntl.c
> @@ -243,6 +243,40 @@ static int f_getowner_uids(struct file *filp, unsigned
> long arg)
> }
> #endif
>
> +long fcntl_rw_hint(struct file *file, unsigned int cmd, unsigned long arg)
The unsigned long arg is a little annoying because it will de different
size for 32-bit vs 64-vit architectures.
How about just doing a get_user and use a fixed-size 64-bit value?
