Re: [Libguestfs] [PATCH v2 nbdkit 5/6] Add truncate filter for truncating or extending the size of plugins.
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
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