A coredump sent over a socket is a plain byte stream. The kernel knows things about the bytes it is sending that a server might care about. For example, it knows where the unpopulated parts of a mapping are. We can't communicate this to userspace currently though.
Add a COREDUMP_HEADER feature bit and a struct coredump_frame_header. Userspace can negotiate that feature. Instead of a byte stream it gets a header plus data. Reassembling the frames yields the same coredump that would have been sent without them. The next patch will introduce a first feature. The frame itself is also versioned and thus extensible with the same protocol as the ack-req sync. A kernel that doesn't know the bit doesn't raise it in coredump_req->mask and a server may not raise a bit the kernel didn't advertise. A server that doesn't know the bit never raises it and gets a plain byte stream. This just adds the infrastructure. Signed-off-by: Christian Brauner (Amutable) <[email protected]> --- include/uapi/linux/coredump.h | 52 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 52 insertions(+) diff --git a/include/uapi/linux/coredump.h b/include/uapi/linux/coredump.h index 662e0468da6e..5252480d3eec 100644 --- a/include/uapi/linux/coredump.h +++ b/include/uapi/linux/coredump.h @@ -11,12 +11,16 @@ * @COREDUMP_USERSPACE: userspace writes coredump * @COREDUMP_REJECT: don't generate coredump * @COREDUMP_WAIT: wait for coredump server + * @COREDUMP_HEADER: send the coredump as a sequence of frames instead of + * as a plain byte stream, see struct coredump_frame_header; + * requires COREDUMP_KERNEL */ enum { COREDUMP_KERNEL = (1ULL << 0), COREDUMP_USERSPACE = (1ULL << 1), COREDUMP_REJECT = (1ULL << 2), COREDUMP_WAIT = (1ULL << 3), + COREDUMP_HEADER = (1ULL << 4), }; /** @@ -101,4 +105,52 @@ enum coredump_mark { __COREDUMP_MARK_MAX = (1U << 31), }; +/** + * enum coredump_frame_type - Type of a coredump frame + * + * @COREDUMP_FRAME_DATA: the header is followed by ->len bytes of data + * @__COREDUMP_FRAME_MAX: the maximum coredump frame type value + */ +enum coredump_frame_type { + COREDUMP_FRAME_DATA = 0U, + __COREDUMP_FRAME_MAX = (1U << 31), +}; + +/** + * struct coredump_frame_header - header of a coredump frame + * @size: size of struct coredump_frame_header + * @type: one of enum coredump_frame_type + * @flags: modifiers for this frame + * @offset: offset of this frame in the coredump + * @len: length of this frame in the coredump + * + * If the coredump server raises COREDUMP_HEADER in coredump_ack->mask the + * kernel doesn't send the coredump as a plain byte stream. It sends a + * sequence of frames instead. A struct coredump_frame_header is followed by + * @len bytes of actual coredump data. + * + * The @size member is set to the size of struct coredump_frame_header the + * kernel knows and lets the header grow later. It comes first so it can be + * peeked. Userspace must consume @size bytes and discard anything beyond + * what it knows. The same way it deals with struct coredump_req. It must + * refuse a @size smaller than COREDUMP_FRAME_HEADER_SIZE_VER0. + * + * The @flags member carries modifiers that change how the frame is to be + * interpreted. No flags are defined yet. Userspace must refuse a frame + * carrying a flag it doesn't know. + * + * COREDUMP_HEADER must be combined with COREDUMP_KERNEL. + */ +struct coredump_frame_header { + __u32 size; + __u32 type; + __u64 flags; + __u64 offset; + __u64 len; +}; + +enum { + COREDUMP_FRAME_HEADER_SIZE_VER0 = 32U, /* size of first published struct */ +}; + #endif /* _UAPI_LINUX_COREDUMP_H */ -- 2.53.0
