[Devel] [PATCH] ploop: show ino and sdev for ploop images in sysfs

[Maxim Patlasov]

Acked-by: Maxim Patlasov <mpatlasov at virtuozzo.com>


On 07/13/2017 05:10 PM, Andrei Vagin wrote:
> Currently we can get an image file for a ploop delta from sysfs, but
> there is a problem, if a ploop was mounted or snapshoted from another
> mount namespace. In this case, we can't report a full path to a delta in
> a current mount namespace, because the origin namespace may be already
> destroyed or a mount with ploop deltas can be mounted into another place
> in the current mntns.
>
> Here is an example of one of such cases:
>
> $ unshare -m ploop mount /mnt/vstorage/test/DiskDescriptor.xml
> Opening delta /mnt/vstorage/test/test
> Opening delta /mnt/vstorage/test/test
> Adding delta dev=/dev/ploop64360 img=/mnt/vstorage/test/test (rw)
>
> $ cat /sys/block/ploop64360/pdelta/0/image
> /test/test
>
> $ cat /sys/block/ploop64360/pdelta/0/image_info
> ino:254
> sdev:0:38
>
> $ stat /mnt/vstorage/test/test
> Device: 26h/38d	Inode: 254         Links: 1
>
> The ploop tool uses delta names to find a proper device by
> Diskdescriptor.xml. Actually, a path to a delta file isn't required in
> this case, it is enough to know a pair of ino and s_dev.
>
> This patch introduces one more file in sysfs, which is called image_info
> and contains an inode number and a source devices for a delta file.
>
> https://jira.sw.ru/browse/PSBM-68404
> Signed-off-by: Andrei Vagin <avagin at openvz.org>
> ---
>   drivers/block/ploop/sysfs.c | 23 +++++++++++++++++++++++
>   1 file changed, 23 insertions(+)
>
> diff --git a/drivers/block/ploop/sysfs.c b/drivers/block/ploop/sysfs.c
> index 0395ccf..acd18ff 100644
> --- a/drivers/block/ploop/sysfs.c
> +++ b/drivers/block/ploop/sysfs.c
> @@ -102,6 +102,22 @@ static ssize_t delta_image_show(struct ploop_delta *delta, char *page)
>   	return len;
>   }
>   
> +static ssize_t delta_image_info_show(struct ploop_delta *delta, char *page)
> +{
> +	int len = -ENOENT;
> +
> +	mutex_lock(&delta->plo->sysfs_mutex);
> +	if (delta->io.files.file) {
> +		struct inode *inode = file_inode(delta->io.files.file);
> +		len = snprintf(page, PAGE_SIZE, "ino:%lu\nsdev:%u:%u\n",
> +				inode->i_ino,
> +				MAJOR(inode->i_sb->s_dev),
> +				MINOR(inode->i_sb->s_dev));
> +	}
> +	mutex_unlock(&delta->plo->sysfs_mutex);
> +	return len;
> +}
> +
>   static ssize_t delta_format_show(struct ploop_delta *delta, char *page)
>   {
>   	return delta_string_show(delta->ops->name, page);
> @@ -147,6 +163,12 @@ static struct delta_sysfs_entry delta_image_entry = {
>   	.store = NULL,
>   };
>   
> +static struct delta_sysfs_entry delta_image_info_entry = {
> +	.attr = {.name = "image_info", .mode = S_IRUGO },
> +	.show = delta_image_info_show,
> +	.store = NULL,
> +};
> +
>   static struct delta_sysfs_entry delta_format_entry = {
>   	.attr = {.name = "format", .mode = S_IRUGO },
>   	.show = delta_format_show,
> @@ -179,6 +201,7 @@ static struct delta_sysfs_entry delta_dump_entry = {
>   static struct attribute *default_attrs[] = {
>   	&delta_level_entry.attr,
>   	&delta_image_entry.attr,
> +	&delta_image_info_entry.attr,
>   	&delta_format_entry.attr,
>   	&delta_io_entry.attr,
>   	&delta_ro_entry.attr,

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