[Libguestfs] [PATCH v2 nbdkit 5/6] Add truncate filter for truncating or extending the size of plugins.
Eric Blake
eblake at redhat.com
Wed Aug 1 16:06:51 UTC 2018
On 08/01/2018 06:10 AM, Richard W.M. Jones wrote:
> This can truncate, extend, or round up/down to a multiple.
> ---
> common-rules.mk | 3 +-
> configure.ac | 1 +
> filters/offset/nbdkit-offset-filter.pod | 7 +-
> filters/partition/nbdkit-partition-filter.pod | 1 +
> filters/truncate/Makefile.am | 61 ++++
> filters/truncate/nbdkit-truncate-filter.pod | 88 +++++
> filters/truncate/truncate.c | 301 ++++++++++++++++++
> 7 files changed, 459 insertions(+), 3 deletions(-)
>
> +
> +=item *
> +
> +Round the size of the plugin up or down to the next multiple of C<N>.
> +Use either C<round-up=N> or C<round-down=N>.
Worth mentioning that N must be a power of 2.
> +
> +#define THREAD_MODEL NBDKIT_THREAD_MODEL_PARALLEL
> +
> +/* These are the parameters. */
> +static int64_t truncate = -1;
> +static unsigned round_up = 0, round_down = 0;
> +
> +/* The real size of the underlying plugin. */
> +static uint64_t real_size;
> +
> +/* The calculated size after applying the parameters. */
> +static uint64_t size;
> +
> +/* This lock protects the real_size and size fields. */
> +static pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;
Do we need the lock, or can we rely on the fact that .prepare will get
called before anything else, and treat these as always initialized after
that point?
> + /* The truncate, round-up and round-down parameters are treated as
> + * separate operations. It's possible to specify more than one,
> + * although perhaps not very useful.
> + */
> + if (truncate >= 0)
> + size = truncate;
> + if (round_up > 0)
> + size = (size + round_up - 1) & ~(round_up-1);
Inconsistent spacing between the two instances of 'round_up - 1'; I
think we favor the spaces everywhere...
> + if (round_down > 0)
> + size &= ~(round_down-1);
...in which case the spacing here is also suspect.
> + if (count > 0) {
> + /* The caller must be writing zeroes, else it's an error. */
> + if (!is_zero (buf, count)) {
> + nbdkit_error ("truncate: write beyond end of underlying device");
> + *err = EIO;
Would ENOSPC be better here?
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
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