[Libguestfs] [PATCH nbdkit v4 08/15] log: Log extents requests.

[Eric Blake]

On 3/26/19 4:17 PM, Richard W.M. Jones wrote:
> Typical output:
> 
> 2019-03-26 18:22:17.287434 connection=2 Extents id=2 offset=0x0 count=0x40000000 req_one=1 ...
> 2019-03-26 18:22:17.290040 connection=2 ...Extents id=2 extents=[{ offset=0x0, length=0x250000, type=0 }, { offset=0x250000, length=0x7db0000, type=3 }, { offset=0x8000000, length=0x8000, type=0 }, { offset=0x8008000, length=0x38000, type=3 }, { offset=0x8040000, length=0x208000, type=0 }, { offset=0x8248000, length=0x7db8000, type=3 }, { offset=0x10000000, length=0x208000, type=0 }, { offset=0x10208000, length=0x7df8000, type=3 }, { offset=0x18000000, length=0x8000, type=0 }, { offset=0x18008000, length=0x38000, type=3 }, { offset=0x18040000, length=0x208000, type=0 }, { offset=0x18248000, length=0x7db8000, type=3 }, { offset=0x20000000, length=0x208000, type=0 }, { offset=0x20208000, length=0x7df8000, type=3 }, { offset=0x28000000, length=0x8000, type=0 }, { offset=0x28008000, length=0x38000, type=3 }, { offset=0x28040000, length=0x208000, type=0 }, { offset=0x28248000, length=0x7db8000, type=3 }, { offset=0x30000000, length=0x208000, type=0 }, { offset=0x30208000, length=0x7df8000, type=3 }, { offset=0x38000000, length=0x8000, type=0 }, { offset=0x38008000, length=0x38000, type=3 }, { offset=0x38040000, length=0x208000, type=0 }, { offset=0x38248000, length=0x7da8000, type=3 }, { offset=0x3fff0000, length=0x10000, type=0 }] return=0
> 
> As you can see this is logging the complete information as generated
> by the underlying plugin, not what is returned to the client (which is
> rather hard for the log filter to discern).  It's probably more useful
> for debugging like this.

Can get quite verbose, but that's par for a logger. If we wanted, we
could introduce a log-abbreviate option, to produce something like:

extents=[{ offset=0x0, length=0x250000, type=0 }, ...N more extents]

where you get verbose by default, but can opt-in to the shorter output.


> +  else {
> +    FILE *fp;
> +    char *extents_str = NULL;
> +    size_t i, n, len = 0;
> +
> +    fp = open_memstream (&extents_str, &len);

Yeah, a memstream makes this easier (it is in POSIX, but not universally
available; do we care?)

Missing a patch to nbdkit-log-filter.pod:

> This filter writes to the file specified by the C<logfile=FILE>
> parameter.  All lines include a timestamp, a connection counter, then
> details about the command.  The following actions are logged: Connect,
> Read, Write, Zero, Trim, Flush, and Disconnect.  Except for Connect

where that sentence needs to be updated.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

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