f2fs: drop exist_data for inline_data when truncated to 0

A test program gets the SEEK_DATA with two values between
a new created file and the exist file on f2fs filesystem.

F2FS filesystem,  (the first "test1" is a new file)
SEEK_DATA size != 0 (offset = 8192)
SEEK_DATA size != 0 (offset = 4096)

PNFS filesystem, (the first "test1" is a new file)
SEEK_DATA size != 0 (offset = 4096)
SEEK_DATA size != 0 (offset = 4096)

int main(int argc, char **argv)
{
        char *filename = argv[1];
        int offset = 1, i = 0, fd = -1;

        if (argc < 2) {
                printf("Usage: %s f2fsfilename\n", argv[0]);
                return -1;
        }

        /*
        if (!access(filename, F_OK) || errno != ENOENT) {
                printf("Needs a new file for test, %m\n");
                return -1;
        }*/

        fd = open(filename, O_RDWR | O_CREAT, 0777);
        if (fd < 0) {
                printf("Create test file %s failed, %m\n", filename);
                return -1;
        }

        for (i = 0; i < 20; i++) {
                offset = 1 << i;
                ftruncate(fd, 0);
                lseek(fd, offset, SEEK_SET);
                write(fd, "test", 5);
                /* Get the alloc size by seek data equal zero*/
                if (lseek(fd, 0, SEEK_DATA)) {
                        printf("SEEK_DATA size != 0 (offset = %d)\n", offset);
                        break;
                }
        }

        close(fd);
        return 0;
}

Reported-and-Tested-by: Kinglong Mee <kinglongmee@gmail.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/file.c

@@ -570,6 +570,8 @@ int truncate_blocks(struct inode *inode, u64 from, bool lock)
 	if (f2fs_has_inline_data(inode)) {
 		if (truncate_inline_inode(ipage, from))
 			set_page_dirty(ipage);
+		if (from == 0)
+			clear_inode_flag(inode, FI_DATA_EXIST);
 		f2fs_put_page(ipage, 1);
 		truncate_page = true;
 		goto out;