[Sheepdog] [RFC] [PATCH] journaling support for atomic operations

[MORITA Kazutaka]

At Mon, 22 Nov 2010 22:55:11 +0530,
Narendra Prasad Madanapalli wrote:
> 
> Hi,
> 
> This patch adds journalling support for sheepdog that can aid in
> performing atomic operations.

Great!

> +#define JRNL_PATH "/journal/"
> +
> +static int  jrnl_init_path(const char *base_path)
> +{
> +	int new, ret;
> +
> +	/* Create journal directory */
> +	jrnl_path = zalloc(strlen(base_path) + strlen(JRNL_PATH) + 1);
> +	sprintf(jrnl_path, "%s" JRNL_PATH, base_path);
> +
> +	ret = init_path(jrnl_path, &new);
> +        /* Error during directory creation */
> +	if (ret)
> +		return ret;
> +	/* If journal is newly created */
> +	if (new)
> +		return 0;
> +
> +	return 0;
> +}

Other functions to initialize directories are named
init_[target]_path(), so this function name should be
init_jrnl_path()?

> +
> +int  jrnl_write_end_mark(jrnl_desc_t  *jd)
> +{
> +	ssize_t  ret;
> +	end_mark_t  end_mark = 1;

The value of end_mark should be defined as a macro, and it should be
more complex value.

> +
> +	ret = pwrite64(jd->jdf_fd, &end_mark, sizeof(end_mark),
> +	               sizeof(jd->jd_head) + jd->jdh_size);
> +
> +	if (ret != sizeof(end_mark)) {
> +		if (errno == ENOSPC)
> +			ret = SD_RES_NO_SPACE;
> +		else
> +			ret = SD_RES_EIO;
> +	} else
> +		ret = SD_RES_SUCCESS;
> +
> +	return ret;
> +}
> +

> +
> +int  jrnl_apply_to_targe_vdi_object(jrnl_file_desc_t *jfd)
> +{
> +	char path[1024], *buf;
> +	int buf_len, res = 0, ret;
> +	ssize_t retsize;
> +	jrnl_head_t jh;
> +
> +	/* FIXME: handle larger size */
> +	buf_len = (1 << 22);
> +	buf = zalloc(buf_len);
> +	if (!buf) {
> +		eprintf("failed to allocate memory\n");
> +		res = SD_RES_NO_MEM;
> +		goto out;
> +	}
> +
> +	/* Open journal */
> +	snprintf(path, sizeof(path), "%s%08u/%016" PRIx64, jrnl_path,
> jfd->jf_epoch, jfd->jf_oid);
> +	ret = jrnl_open(jfd, O_RDONLY);
> +	if (ret) {
> +		res = SD_RES_EIO;
> +		goto freemem;
> +	}
> +
> +	/* Flush out journal to disk (vdi object) */
> +	retsize = pread64(jfd->jf_fd, &jh, sizeof(jh), 0);
> +	retsize = pread64(jfd->jf_fd, buf, jh.jh_size, sizeof(jh));

We should check that the journal has an end mark here.

> +	retsize = pwrite64(jfd->jf_vdi_fd, buf, jh.jh_size, jh.jh_offset);
> +
> +	/* Clean up */
> +	close(jfd->jf_fd);
> +	jfd->jf_fd = 0;
> +freemem:
> +	free(buf);
> +out:
> +	return res;
> +}
> +
> +int  jrnl_writte_data_to_targe_vdi_object(jrnl_file_desc_t *jfd, void *data)
> +{
> +	//
> +	// FIXME: Need to implement this function
> +	//
> +
> +	return 0;
> +}

What's the difference between jrnl_apply_to_targe_vdi_object() and
jrnl_write_data_to_target_vdi_object()?  When do we use
jrnl_write_data_to_target_vdi_object()?

> +
> +int  jrnl_recover_vdis()
> +{
> +	DIR *dir;
> +	struct dirent *d;
> +	char jrnl_dir[1024], jrnl_file_path[1024];
> +	int  epoch;
> +
> +	epoch = get_latest_epoch();
> +	if (epoch < 0) {
> +		return 1;
> +	}
> +	snprintf(jrnl_dir, sizeof(jrnl_dir), "%s%08u", jrnl_path, epoch);
> +
> +	dir = opendir(jrnl_dir);
> +	if (!dir)
> +		return -1;
> +
> +	/* TODO: Not complete as error handling to be added */
> +	while ((d = readdir(dir))) {
> +		jrnl_file_desc_t  jfd;
> +		jfd.jf_oid = atoi(d->d_name);
> +		snprintf(jrnl_file_path, sizeof(jrnl_file_path), "%s%016" PRIx64,
> jrnl_dir, jfd.jf_oid);
> +		jrnl_open(&jfd, O_RDONLY);
> +		jrnl_apply_to_targe_vdi_object(&jfd);
> +	}
> +	closedir(dir);
> +
> +	return 0;
> +}
> +

I think the followings are not implemented yet, yes?

 - remove a journal file when it becomes unnecessary
 - apply journal data before accessing a vdi object if the journal file
   exists


Thanks,

Kazutaka