• Jens Axboe's avatar
    fs: add fcntl() interface for setting/getting write life time hints · c75b1d94
    Jens Axboe authored
    Define a set of write life time hints:
    RWH_WRITE_LIFE_NOT_SET	No hint information set
    RWH_WRITE_LIFE_NONE	No hints about write life time
    RWH_WRITE_LIFE_SHORT	Data written has a short life time
    RWH_WRITE_LIFE_MEDIUM	Data written has a medium life time
    RWH_WRITE_LIFE_LONG	Data written has a long life time
    RWH_WRITE_LIFE_EXTREME	Data written has an extremely long life time
    The intent is for these values to be relative to each other, no
    absolute meaning should be attached to these flag names.
    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 on the
    			underlying inode.
    F_SET_RW_HINT		Set one of the above write hints on the
    			underlying inode.
    F_GET_FILE_RW_HINT	Returns the read/write hint set on the
    			file descriptor.
    F_SET_FILE_RW_HINT	Set one of the above write hints on the
    			file descriptor.
    The user passes in a 64-bit pointer to get/set these values, and
    the interface returns 0/-1 on success/error.
    Sample program testing/implementing basic setting/getting of write
    hints is below.
    Add support for storing the write life time hint in the inode flags
    and in struct file as well, and pass them to the kiocb flags. If
    both a file and its corresponding inode has a write hint, then we
    use the one in the file, if available. The file hint can be used
    for sync/direct IO, for buffered writeback only the inode hint
    is available.
    This is in preparation for utilizing these hints in the block layer,
    to guide on-media data placement.
     * writehint.c: get or set an inode write hint
     #include <stdio.h>
     #include <fcntl.h>
     #include <stdlib.h>
     #include <unistd.h>
     #include <stdbool.h>
     #include <inttypes.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)
    static char *str[] = { "RWF_WRITE_LIFE_NOT_SET", "RWH_WRITE_LIFE_NONE",
    int main(int argc, char *argv[])
    	uint64_t hint;
    	int fd, ret;
    	if (argc < 2) {
    		fprintf(stderr, "%s: file <hint>\n", argv[0]);
    		return 1;
    	fd = open(argv[1], O_RDONLY);
    	if (fd < 0) {
    		return 2;
    	if (argc > 2) {
    		hint = atoi(argv[2]);
    		ret = fcntl(fd, F_SET_RW_HINT, &hint);
    		if (ret < 0) {
    			perror("fcntl: F_SET_RW_HINT");
    			return 4;
    	ret = fcntl(fd, F_GET_RW_HINT, &hint);
    	if (ret < 0) {
    		perror("fcntl: F_GET_RW_HINT");
    		return 3;
    	printf("%s: hint %s\n", argv[1], str[hint]);
    	return 0;
    Reviewed-by: 's avatarMartin K. Petersen <martin.petersen@oracle.com>
    Signed-off-by: 's avatarJens Axboe <axboe@kernel.dk>
fcntl.c 21.8 KB