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authorThomas Schwinge <tschwinge@gnu.org>2009-05-20 10:49:07 +0200
committerThomas Schwinge <tschwinge@gnu.org>2009-05-20 10:49:07 +0200
commitf90c5b8e926cad2bd21e93c523be5a1776e11796 (patch)
tree8b184df0904c50a7cdfde98781b4bb8af8a4097e /hurd/libstore
parentca4f4b137695e989666ddc7d5344d8d07532ec54 (diff)
Text from a 2000-12-21 email by Roland McGrath.
Message-Id: <200012210724.eBL7OHv09671@neuralgia.linnaean.org>
Diffstat (limited to 'hurd/libstore')
-rw-r--r--hurd/libstore/copy_store.mdwn13
-rw-r--r--hurd/libstore/zero_store.mdwn9
2 files changed, 20 insertions, 2 deletions
diff --git a/hurd/libstore/copy_store.mdwn b/hurd/libstore/copy_store.mdwn
index 808470ec..c0a25d7d 100644
--- a/hurd/libstore/copy_store.mdwn
+++ b/hurd/libstore/copy_store.mdwn
@@ -1,4 +1,4 @@
-[[!meta copyright="Copyright © 2007, 2008, 2009 Free Software Foundation,
+[[!meta copyright="Copyright © 2000, 2007, 2008, 2009 Free Software Foundation,
Inc."]]
[[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable
@@ -10,3 +10,14 @@ is included in the section entitled [[GNU Free Documentation
License|/fdl]]."]]"""]]
[[!meta title="copy store: copy-on-write; discard changes on termination"]]
+
+A *copy* store is meaningful only with respect to a child store. What a *copy*
+store does is to read the child store's entire contents into memory at startup
+time and then use that buffer as the contents of the store thereafter. (The
+code for this is in `libstore/copy.c`.)
+
+Because of how the interfaces are specified, reading the entire contents of a
+[[*zero* store|zero store]] in fact means just `vm_allocate`ing fresh memory.
+So, a *copy* store based on a [[*zero* store|zero store]] is just what you'd
+get from `vm_allocate`ing some memory and passing it into
+`store_buffer_create`.
diff --git a/hurd/libstore/zero_store.mdwn b/hurd/libstore/zero_store.mdwn
index 120847ba..4c53ab56 100644
--- a/hurd/libstore/zero_store.mdwn
+++ b/hurd/libstore/zero_store.mdwn
@@ -1,4 +1,4 @@
-[[!meta copyright="Copyright © 2007, 2008, 2009 Free Software Foundation,
+[[!meta copyright="Copyright © 2000, 2007, 2008, 2009 Free Software Foundation,
Inc."]]
[[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable
@@ -10,3 +10,10 @@ is included in the section entitled [[GNU Free Documentation
License|/fdl]]."]]"""]]
[[!meta title="zero store: empty block device"]]
+
+A *zero* store is what `/dev/zero` is (always reads zeros), the setting on
+`/dev/zero` gives no name (i.e. size) and the default size is the maximum
+possible. The only meaning of the size of a *zero* is what `st_size` will
+report and what offsets it will let you try to read or write from--there is
+never any data associated with a *zero* store. (The code for this is in
+`libstore/zero.c`.)