126 lines
4.5 KiB
Diff
126 lines
4.5 KiB
Diff
From 2a3e909e9e1ccb608bde75b76524acd753b33889 Mon Sep 17 00:00:00 2001
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From: "Richard W.M. Jones" <rjones@redhat.com>
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Date: Sat, 25 Jan 2020 11:38:14 +0000
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Subject: [PATCH 12/19] extentlist: Documentation and test fixes.
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Updates commit 3e770b6d6620a62546849a2863638041c0b00640.
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(cherry picked from commit c16709ef663a5ed9fd9ddef4e379f316d84c9a07)
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---
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TODO | 12 +++++++----
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.../extentlist/nbdkit-extentlist-filter.pod | 21 +++++++++++++------
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plugins/curl/nbdkit-curl-plugin.pod | 1 +
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plugins/ssh/nbdkit-ssh-plugin.pod | 1 +
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tests/test-extentlist.sh | 2 +-
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5 files changed, 26 insertions(+), 11 deletions(-)
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diff --git a/TODO b/TODO
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index 2a3e89dc..e1ac71cd 100644
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--- a/TODO
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+++ b/TODO
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@@ -187,10 +187,6 @@ Suggestions for filters
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MBs of extra data)
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https://github.com/facebook/zstd/issues/395#issuecomment-535875379
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-* nbdkit-extentlist-filter could read the extents generated by
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- qemu-img map, allowing extents to be ported from a qemu block
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- device.
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-
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nbdkit-rate-filter:
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* allow other kinds of traffic shaping such as VBR
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@@ -216,6 +212,14 @@ nbdkit-retry-filter:
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* subsecond times
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+nbdkit-extentlist-filter:
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+
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+* read the extents generated by qemu-img map, allowing extents to be
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+ ported from a qemu block device
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+
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+* make non-read-only access safe by updating the extent list when the
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+ filter sees writes and trims
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+
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Filters for security
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--------------------
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diff --git a/filters/extentlist/nbdkit-extentlist-filter.pod b/filters/extentlist/nbdkit-extentlist-filter.pod
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index adfb4ad8..5d1a38ae 100644
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--- a/filters/extentlist/nbdkit-extentlist-filter.pod
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+++ b/filters/extentlist/nbdkit-extentlist-filter.pod
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@@ -4,7 +4,7 @@ nbdkit-extentlist-filter - place extent list over a plugin
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=head1 SYNOPSIS
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- nbdkit --filter=extentlist plugin extentlist=FILENAME
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+ nbdkit -r --filter=extentlist plugin extentlist=FILENAME
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=head1 DESCRIPTION
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@@ -13,11 +13,20 @@ static list of extents on top of an existing plugin. Extents record
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whether or not specific parts of the disk are allocated or sparse.
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You can use this with plugins which cannot get extent information
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-themselves, but you can get this information from another source. One
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-place where it is useful is with L<nbdkit-ssh-plugin(1)> because the
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-sftp protocol does not support reading sparseness information, but you
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-may be able to get this information directly from the source disk on
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-the remote server.
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+themselves, but where you can get this information from another
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+source. One place where it is useful is with L<nbdkit-ssh-plugin(1)>
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+because the sftp protocol does not support reading sparseness
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+information, but you may be able to get this information directly from
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+the source disk on the remote server using commands such as
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+L<xfs_bmap(8)>. A similar situation applies to
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+L<nbdkit-curl-plugin(1)>.
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+
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+Note that the extent list is read-only. This filter does not monitor
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+writes and trims in order to update the extent list. What can happen
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+is that you would write to a “hole” in the disk, but would not be able
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+to read it back because the NBD client would still think that part of
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+the disk is a hole. So it is generally only safe to use this filter
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+in read-only mode (I<-r> option).
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=head1 FILE FORMAT
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diff --git a/plugins/curl/nbdkit-curl-plugin.pod b/plugins/curl/nbdkit-curl-plugin.pod
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index 827e0bd1..d3c85248 100644
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--- a/plugins/curl/nbdkit-curl-plugin.pod
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+++ b/plugins/curl/nbdkit-curl-plugin.pod
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@@ -182,6 +182,7 @@ L<libcurl(3)>,
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L<CURLOPT_COOKIE(3)>
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L<CURLOPT_VERBOSE(3)>,
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L<nbdkit(1)>,
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+L<nbdkit-extentlist-filter(1)>,
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L<nbdkit-readahead-filter(1)>,
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L<nbdkit-retry-filter(1)>,
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L<nbdkit-ssh-plugin(1)>,
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diff --git a/plugins/ssh/nbdkit-ssh-plugin.pod b/plugins/ssh/nbdkit-ssh-plugin.pod
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index 0a0421d5..3fc3146a 100644
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--- a/plugins/ssh/nbdkit-ssh-plugin.pod
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+++ b/plugins/ssh/nbdkit-ssh-plugin.pod
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@@ -316,6 +316,7 @@ C<nbdkit-ssh-plugin> first appeared in nbdkit 1.12.
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L<nbdkit(1)>,
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L<nbdkit-curl-plugin(1)>,
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+L<nbdkit-extentlist-filter(1)>,
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L<nbdkit-readahead-filter(1)>,
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L<nbdkit-retry-filter(1)>,
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L<nbdkit-plugin(3)>,
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diff --git a/tests/test-extentlist.sh b/tests/test-extentlist.sh
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index 7d05de4f..73ce3ca6 100755
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--- a/tests/test-extentlist.sh
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+++ b/tests/test-extentlist.sh
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@@ -50,7 +50,7 @@ cleanup_fn rm $files
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test ()
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{
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nbdkit -v -D extentlist.lookup=1 \
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- -U - \
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+ -r -U - \
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--filter=extentlist \
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null size=$1 extentlist=$input \
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--run 'qemu-img map -f raw --output=json $nbd' |
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--
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2.18.2
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