[Xen-devel] Re: xl: Add subcommand 'xl dmesg'

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Ian Jackson writes ("[Xen-devel] Re: xl: Add subcommand 'xl dmesg'"):
> Are we sure that calling the logging function for every line in the
> ring is really what we want ?  If nothing else this will repeat
> messages.

Having thought about this some more (and had a chat with Stefano) I
think the right libxl interface is an iterator, something like this:

 struct libxl_xen_console_reader*
 libxl_xen_console_read_start(struct libxl_ctx*);

 int
 libxl_xen_console_read_line(struct libxl_ctx*,
                             struct libxl_xen_console_reader*,
                             char **line_r);
   /* return values:                                          *line_r
    *   1          success, whole line obtained from buffer    non-0
    *   0          no more lines available right now           0
    *   negative   error code ERROR_*                          0
    * On success *line_r is updated to point to a nul-terminated
    * string which is valid until the next call on the same console
    * reader.  The libxl caller may overwrite parts of the string
    * if it wishes. */

 void
 libxl_xen_console_read_finish(struct libxl_ctx*,
                               struct libxl_xen_console_reader*);

"xl dmesg" then calls _start, loops calling line, and then calls
_finish.  Other libxl callers can plumb it into logging or poll for
more output of whatever they like.

Ian.

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