On Tue, 18 Oct 2022 at 12:36, Muhammad Usama Anjum
<usama.anjum@xxxxxxxxxxxxx> wrote:
[...]
> I've included the masks which the CRIU developers have specified.
> max_out_page is another new optional variable which is needed to
> terminate the operation without visiting all the pages after finding the
> max_out_page number of desired pages. There is no way to terminate the
> operation without this variable.
>
> How does the interface looks now? Please comment.
>
> /* PAGEMAP IOCTL */
> #define PAGEMAP_GET _IOWR('f', 16, struct pagemap_sd_args)
> #define PAGEMAP_CLEAR _IOWR('f', 17, struct pagemap_sd_args)
> #define PAGEMAP_GET_AND_CLEAR _IOWR('f', 18, struct pagemap_sd_args)
Why are three IOCTLs needed? Could CLEAR be a flag (like the
PAGEMAP_NO_REUSED_REGIONS) or 'cmask' and GET be implied when vec !=
NULL?
> /* Bits are set in the bitmap of the page_region and masks in
> pagemap_sd_args */
> #define PAGE_IS_SD 1 << 0
> #define PAGE_IS_FILE 1 << 1
> #define PAGE_IS_PRESENT 1 << 2
> #define PAGE_IS_SWAPED 1 << 3
>
> /**
> * struct page_region - Page region with bitmap flags
> * @start: Start of the region
> * @len: Length of the region
> * bitmap: Bits sets for the region
> */
> struct page_region {
> __u64 start;
> __u64 len;
> __u64 bitmap;
> };
Could you explain what units start and len are using? Are they bytes
or pages (what size)?
> /**
> * struct pagemap_sd_args - Soft-dirty IOCTL argument
Nit: it's not soft-dirty-specific anymore. Maybe "pagemap_scan_args"?
> * @start: Starting address
> * @len: Length of the region
> * @vec: Output page_region struct array
> * @vec_len: Length of the page_region struct array
> * @max_out_page: Optional max output pages (It must be less than
> vec_len if specified)
Why is it required to be less than vec_len? vec_len effectively
specifies max number of ranges to find, and this new additional field
counts pages, I suppose?
BTW, if we count pages, then what size of them? Maybe using bytes
(matching start/len fields) would be more consistent?
> * @flags: Special flags for the IOCTL
> * @rmask: Special flags for the IOCTL
> * @amask: Special flags for the IOCTL
> * @emask: Special flags for the IOCTL
> * @__reserved: Reserved member to preserve data alignment. Must be 0.
> */
> struct pagemap_sd_args {
> __u64 __user start;
> __u64 len;
> __u64 __user vec; // page_region
> __u64 vec_len; // sizeof(page_region)
> __u32 flags; // special flags
> __u32 rmask;
> __u32 amask;
> __u32 emask;
> __u32 max_out_page;
> __u32 __reserved;
> };
>
> /* Special flags */
> #define PAGEMAP_NO_REUSED_REGIONS 0x1
What does this flag do?
Best Regards
Michał Mirosław
