152 lines
5.0 KiB
Diff
152 lines
5.0 KiB
Diff
From 4db23fd29af0488aa9c7e01577a5be9565a4465e Mon Sep 17 00:00:00 2001
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From: "Richard W.M. Jones" <rjones@redhat.com>
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Date: Mon, 26 Jul 2021 16:16:15 +0100
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Subject: [PATCH] cache: Implement cache-on-read=/PATH
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For virt-v2v we will need to be able to turn cache-on-read on while
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performing inspection and modification of the guest, and off when
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doing the bulk copy. To do that allow the cache-on-read parameter to
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refer to a path where the existence of the path toggles the feature.
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(We could restart nbdkit between these phases, but this change avoids
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doing that.)
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(cherry picked from commit c8b575241b15b3bf0adaf15313e67e5ed4270b5a)
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---
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filters/cache/blk.c | 2 +-
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filters/cache/cache.c | 33 ++++++++++++++++++++-------
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filters/cache/cache.h | 10 ++++++--
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filters/cache/nbdkit-cache-filter.pod | 11 ++++++++-
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4 files changed, 44 insertions(+), 12 deletions(-)
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diff --git a/filters/cache/blk.c b/filters/cache/blk.c
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index 42bd3779..19f79605 100644
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--- a/filters/cache/blk.c
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+++ b/filters/cache/blk.c
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@@ -244,7 +244,7 @@ _blk_read_multiple (nbdkit_next *next,
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memset (block + n, 0, tail);
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/* If cache-on-read, copy the blocks to the cache. */
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- if (cache_on_read) {
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+ if (cache_on_read ()) {
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if (cache_debug_verbose)
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nbdkit_debug ("cache: cache-on-read block %" PRIu64
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" (offset %" PRIu64 ")",
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diff --git a/filters/cache/cache.c b/filters/cache/cache.c
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index 14cc03f2..44da0008 100644
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--- a/filters/cache/cache.c
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+++ b/filters/cache/cache.c
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@@ -74,7 +74,8 @@ unsigned blksize;
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enum cache_mode cache_mode = CACHE_MODE_WRITEBACK;
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int64_t max_size = -1;
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unsigned hi_thresh = 95, lo_thresh = 80;
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-bool cache_on_read = false;
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+enum cor_mode cor_mode = COR_OFF;
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+const char *cor_path;
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static int cache_flush (nbdkit_next *next, void *handle, uint32_t flags,
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int *err);
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@@ -161,12 +162,16 @@ cache_config (nbdkit_next_config *next, nbdkit_backend *nxdata,
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}
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#endif /* !HAVE_CACHE_RECLAIM */
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else if (strcmp (key, "cache-on-read") == 0) {
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- int r;
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-
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- r = nbdkit_parse_bool (value);
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- if (r == -1)
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- return -1;
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- cache_on_read = r;
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+ if (value[0] == '/') {
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+ cor_path = value;
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+ cor_mode = COR_PATH;
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+ }
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+ else {
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+ int r = nbdkit_parse_bool (value);
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+ if (r == -1)
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+ return -1;
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+ cor_mode = r ? COR_ON : COR_OFF;
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+ }
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return 0;
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}
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else {
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@@ -177,7 +182,7 @@ cache_config (nbdkit_next_config *next, nbdkit_backend *nxdata,
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#define cache_config_help_common \
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"cache=MODE Set cache MODE, one of writeback (default),\n" \
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" writethrough, or unsafe.\n" \
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- "cache-on-read=BOOL Set to true to cache on reads (default false).\n"
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+ "cache-on-read=BOOL|/PATH Set to true to cache on reads (default false).\n"
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#ifndef HAVE_CACHE_RECLAIM
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#define cache_config_help cache_config_help_common
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#else
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@@ -187,6 +192,18 @@ cache_config (nbdkit_next_config *next, nbdkit_backend *nxdata,
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"cache-low-threshold=PCT Percentage of max size where reclaim ends.\n"
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#endif
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+/* Decide if cache-on-read is currently on or off. */
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+bool
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+cache_on_read (void)
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+{
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+ switch (cor_mode) {
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+ case COR_ON: return true;
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+ case COR_OFF: return false;
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+ case COR_PATH: return access (cor_path, F_OK) == 0;
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+ default: abort ();
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+ }
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+}
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+
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static int
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cache_config_complete (nbdkit_next_config_complete *next,
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nbdkit_backend *nxdata)
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diff --git a/filters/cache/cache.h b/filters/cache/cache.h
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index 2b72221f..a559adef 100644
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--- a/filters/cache/cache.h
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+++ b/filters/cache/cache.h
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@@ -49,7 +49,13 @@ extern unsigned blksize;
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extern int64_t max_size;
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extern unsigned hi_thresh, lo_thresh;
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-/* Cache read requests. */
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-extern bool cache_on_read;
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+/* Cache on read mode. */
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+extern enum cor_mode {
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+ COR_OFF,
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+ COR_ON,
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+ COR_PATH,
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+} cor_mode;
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+extern const char *cor_path;
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+extern bool cache_on_read (void);
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#endif /* NBDKIT_CACHE_H */
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diff --git a/filters/cache/nbdkit-cache-filter.pod b/filters/cache/nbdkit-cache-filter.pod
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index ebcf1d10..f20cb9ce 100644
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--- a/filters/cache/nbdkit-cache-filter.pod
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+++ b/filters/cache/nbdkit-cache-filter.pod
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@@ -8,7 +8,7 @@ nbdkit-cache-filter - nbdkit caching filter
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[cache-max-size=SIZE]
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[cache-high-threshold=N]
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[cache-low-threshold=N]
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- [cache-on-read=true|false]
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+ [cache-on-read=true|false|/PATH]
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[plugin-args...]
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=head1 DESCRIPTION
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@@ -87,6 +87,15 @@ the plugin.
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Do not cache read requests (this is the default).
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+=item B<cache-on-read=/PATH>
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+
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+(nbdkit E<ge> 1.28)
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+
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+When F</PATH> (which must be an absolute path) exists, this behaves
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+like C<cache-on-read=true>, and when it does not exist like
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+C<cache-on-read=false>. This allows you to control the cache-on-read
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+behaviour while nbdkit is running.
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+
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=back
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=head1 CACHE MAXIMUM SIZE
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--
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2.31.1
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