On 06/26/2017 10:09 AM, Darrick J. Wong wrote:
> On Mon, Jun 26, 2017 at 07:55:27AM -0600, Jens Axboe wrote:
>> On 06/26/2017 03:51 AM, Christoph Hellwig wrote:
>>> Please document the userspace API (added linux-api and linux-man
>>> to CC for sugestions), especially including the odd effects of the
>>> per-inode settings.
>>
>> Of course, I'll send in a diff for the fcntl(2) man page.
>>
>>> Also I would highly recommend to use different fcntl commands
>>> for the file vs inode hints to avoid any strange behavior.
>>
>> OK, used to have that too... I can add specific _FILE versions.
>
> While you're at it, can you also send in an xfstest or two to check the
> basic functionality of the fcntl so that we know the code reflects the
> userspace API ("I set this hint and now I can query it back" and "file
> hint overrides inode hint") that we want?
I definitely can. I already wrote the below to verify that it behaves
the way it should.
/*
* test-writehints.c: test file/inode write hint setting/getting
*/
#include <stdio.h>
#include <fcntl.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdbool.h>
#include <inttypes.h>
#include <assert.h>
#ifndef F_GET_RW_HINT
#define F_LINUX_SPECIFIC_BASE 1024
#define F_GET_RW_HINT (F_LINUX_SPECIFIC_BASE + 11)
#define F_SET_RW_HINT (F_LINUX_SPECIFIC_BASE + 12)
#define F_GET_FILE_RW_HINT (F_LINUX_SPECIFIC_BASE + 13)
#define F_SET_FILE_RW_HINT (F_LINUX_SPECIFIC_BASE + 14)
#define RWF_WRITE_LIFE_NOT_SET 0
#define RWH_WRITE_LIFE_NONE 1
#define RWH_WRITE_LIFE_SHORT 2
#define RWH_WRITE_LIFE_MEDIUM 3
#define RWH_WRITE_LIFE_LONG 4
#define RWH_WRITE_LIFE_EXTREME 5
#endif
static int __get_write_hint(int fd, int cmd)
{
uint64_t hint;
int ret;
ret = fcntl(fd, cmd, &hint);
if (ret < 0) {
perror("fcntl: F_GET_RW_FILE_HINT");
return -1;
}
return hint;
}
static int get_file_write_hint(int fd)
{
return __get_write_hint(fd, F_GET_FILE_RW_HINT);
}
static int get_inode_write_hint(int fd)
{
return __get_write_hint(fd, F_GET_RW_HINT);
}
static void set_file_write_hint(int fd, uint64_t hint)
{
uint64_t set_hint = hint;
int ret;
ret = fcntl(fd, F_SET_FILE_RW_HINT, &set_hint);
if (ret < 0) {
perror("fcntl: F_RW_SET_HINT");
return;
}
}
static void set_inode_write_hint(int fd, uint64_t hint)
{
uint64_t set_hint = hint;
int ret;
ret = fcntl(fd, F_SET_RW_HINT, &set_hint);
if (ret < 0) {
perror("fcntl: F_RW_SET_HINT");
return;
}
}
int main(int argc, char *argv[])
{
char filename[] = "/tmp/writehintsXXXXXX";
int ihint, fhint, fd;
fd = open(filename, O_RDWR | O_CREAT | 0644);
if (fd < 0) {
perror("open");
return 2;
}
/*
* Default hints for both file and inode should be NOT_SET
*/
fhint = get_file_write_hint(fd);
if (fhint < 0)
return 0;
ihint = get_inode_write_hint(fd);
assert(fhint == ihint);
assert(fhint == RWF_WRITE_LIFE_NOT_SET);
/*
* Set inode hint, check file hint returns the right hint
*/
set_inode_write_hint(fd, RWH_WRITE_LIFE_SHORT);
fhint = get_file_write_hint(fd);
ihint = get_inode_write_hint(fd);
assert(fhint == ihint);
assert(fhint == RWH_WRITE_LIFE_SHORT);
/*
* Now set file hint, ensure that this is now the hint we get
*/
set_file_write_hint(fd, RWH_WRITE_LIFE_LONG);
fhint = get_file_write_hint(fd);
ihint = get_inode_write_hint(fd);
assert(fhint == RWH_WRITE_LIFE_LONG);
assert(ihint == RWH_WRITE_LIFE_SHORT);
/*
* Clear inode write hint, ensure that file still returns the set hint
*/
set_inode_write_hint(fd, RWF_WRITE_LIFE_NOT_SET);
fhint = get_file_write_hint(fd);
ihint = get_inode_write_hint(fd);
assert(fhint == RWH_WRITE_LIFE_LONG);
assert(ihint == RWF_WRITE_LIFE_NOT_SET);
/*
* Clear file write hint, ensure that now returns cleared
*/
set_file_write_hint(fd, RWF_WRITE_LIFE_NOT_SET);
fhint = get_file_write_hint(fd);
assert(fhint == RWF_WRITE_LIFE_NOT_SET);
close(fd);
unlink(filename);
return 0;
}
--
Jens Axboe
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