On 06/19/2017 12:28 AM, Christoph Hellwig wrote:
> 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 <axboe@xxxxxxxxx>
>> ---
>> 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?
It's just passing it in from fcnt(), my intent was for it to be a u32 on the
uapi side. But we can make it a 64-bit type, since we're going away from
the enum and making it a proper type.
--
Jens Axboe
