12:28 p.m.
For virt-v2v we will need to be able to turn cache-on-read on while
performing inspection and modification of the guest, and later off
when doing the bulk copy. To do that allow the cache-on-read
parameter to refer to a path where the existence of the path toggles
the feature.
(We could restart nbdkit between these phases, but this change avoids
doing that.)
---
filters/cache/nbdkit-cache-filter.pod | 11 ++++++++-
filters/cache/cache.h | 10 ++++++--
filters/cache/blk.c | 2 +-
filters/cache/cache.c | 33 ++++++++++++++++++++-------
4 files changed, 44 insertions(+), 12 deletions(-)
diff --git a/filters/cache/nbdkit-cache-filter.pod
b/filters/cache/nbdkit-cache-filter.pod
index 34fd0b29..2ac307e0 100644
--- a/filters/cache/nbdkit-cache-filter.pod
+++ b/filters/cache/nbdkit-cache-filter.pod
@@ -8,7 +8,7 @@ nbdkit-cache-filter - nbdkit caching filter
[cache-max-size=SIZE]
[cache-high-threshold=N]
[cache-low-threshold=N]
- [cache-on-read=true|false]
+ [cache-on-read=true|false|/PATH]
[plugin-args...]
=head1 DESCRIPTION
@@ -87,6 +87,15 @@ the plugin.
Do not cache read requests (this is the default).
+=item B<cache-on-read=/PATH>
+
+(nbdkit E<ge> 1.28)
+
+When F</PATH> (which must be an absolute path) exists, this behaves
+like C<cache-on-read=true>, and when it does not exist like
+C<cache-on-read=false>. This allows you to control the cache-on-read
+behaviour while nbdkit is running.
+
=back
=head1 CACHE MAXIMUM SIZE
diff --git a/filters/cache/cache.h b/filters/cache/cache.h
index 2b72221f..a559adef 100644
--- a/filters/cache/cache.h
+++ b/filters/cache/cache.h
@@ -49,7 +49,13 @@ extern unsigned blksize;
extern int64_t max_size;
extern unsigned hi_thresh, lo_thresh;
-/* Cache read requests. */
-extern bool cache_on_read;
+/* Cache on read mode. */
+extern enum cor_mode {
+ COR_OFF,
+ COR_ON,
+ COR_PATH,
+} cor_mode;
+extern const char *cor_path;
+extern bool cache_on_read (void);
#endif /* NBDKIT_CACHE_H */
diff --git a/filters/cache/blk.c b/filters/cache/blk.c
index 42bd3779..19f79605 100644
--- a/filters/cache/blk.c
+++ b/filters/cache/blk.c
@@ -244,7 +244,7 @@ _blk_read_multiple (nbdkit_next *next,
memset (block + n, 0, tail);
/* If cache-on-read, copy the blocks to the cache. */
- if (cache_on_read) {
+ if (cache_on_read ()) {
if (cache_debug_verbose)
nbdkit_debug ("cache: cache-on-read block %" PRIu64
" (offset %" PRIu64 ")",
diff --git a/filters/cache/cache.c b/filters/cache/cache.c
index 9c081948..8af52106 100644
--- a/filters/cache/cache.c
+++ b/filters/cache/cache.c
@@ -74,7 +74,8 @@ unsigned blksize;
enum cache_mode cache_mode = CACHE_MODE_WRITEBACK;
int64_t max_size = -1;
unsigned hi_thresh = 95, lo_thresh = 80;
-bool cache_on_read = false;
+enum cor_mode cor_mode = COR_OFF;
+const char *cor_path;
static int cache_flush (nbdkit_next *next, void *handle, uint32_t flags,
int *err);
@@ -161,12 +162,16 @@ cache_config (nbdkit_next_config *next, nbdkit_backend *nxdata,
}
#endif /* !HAVE_CACHE_RECLAIM */
else if (strcmp (key, "cache-on-read") == 0) {
- int r;
-
- r = nbdkit_parse_bool (value);
- if (r == -1)
- return -1;
- cache_on_read = r;
+ if (value[0] == '/') {
+ cor_path = value;
+ cor_mode = COR_PATH;
+ }
+ else {
+ int r = nbdkit_parse_bool (value);
+ if (r == -1)
+ return -1;
+ cor_mode = r ? COR_ON : COR_OFF;
+ }
return 0;
}
else {
@@ -177,7 +182,7 @@ cache_config (nbdkit_next_config *next, nbdkit_backend *nxdata,
#define cache_config_help_common \
"cache=MODE Set cache MODE, one of writeback (default),\n" \
" writethrough, or unsafe.\n" \
- "cache-on-read=BOOL Set to true to cache on reads (default false).\n"
+ "cache-on-read=BOOL|/PATH Set to true to cache on reads (default false).\n"
#ifndef HAVE_CACHE_RECLAIM
#define cache_config_help cache_config_help_common
#else
@@ -187,6 +192,18 @@ cache_config (nbdkit_next_config *next, nbdkit_backend *nxdata,
"cache-low-threshold=PCT Percentage of max size where reclaim ends.\n"
#endif
+/* Decide if cache-on-read is currently on or off. */
+bool
+cache_on_read (void)
+{
+ switch (cor_mode) {
+ case COR_ON: return true;
+ case COR_OFF: return false;
+ case COR_PATH: return access (cor_path, F_OK) == 0;
+ default: abort ();
+ }
+}
+
static int
cache_config_complete (nbdkit_next_config_complete *next,
nbdkit_backend *nxdata)
--
2.32.0