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From 91db4de9f068eb7d90f30e1d7205b3f0c988cce7 Mon Sep 17 00:00:00 2001
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From: "Richard W.M. Jones" <rjones@redhat.com>
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Date: Fri, 12 Aug 2016 10:32:26 +0100
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Subject: [PATCH] v2v: Make fstrim warning clearer (RHBZ#1366456).
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This reverts the change made for RHBZ#1168144. The warning is now
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always displayed.
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It would be nice to make the warning actionable, but there is not a
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lot that end users can do since fstrim is such a complex topic
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interacting with all filesystem and storage layers.
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(cherry picked from commit 66816e11332b07a07efd6821e7ecf090691ce441)
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---
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v2v/v2v.ml | 6 +-----
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v2v/virt-v2v.pod | 26 ++++++++++++++++++++++++++
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2 files changed, 27 insertions(+), 5 deletions(-)
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diff --git a/v2v/v2v.ml b/v2v/v2v.ml
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index 4b06bc1..21f8d77 100644
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--- a/v2v/v2v.ml
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+++ b/v2v/v2v.ml
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@@ -425,11 +425,7 @@ and do_fstrim g no_trim inspect =
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if mounted then (
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try g#fstrim "/"
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with G.Error msg ->
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- (* Only emit this warning when debugging, because otherwise
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- * it causes distress (RHBZ#1168144).
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- *)
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- if verbose () then
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- warning (f_"%s (ignored)") msg
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+ warning (f_"fstrim on guest filesystem %s failed. Usually you can ignore this message. To find out more read \"Trimming\" in virt-v2v(1).\n\nOriginal message: %s") dev msg
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)
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) fses
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diff --git a/v2v/virt-v2v.pod b/v2v/virt-v2v.pod
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index 9fc0b72..434f57e 100644
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--- a/v2v/virt-v2v.pod
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+++ b/v2v/virt-v2v.pod
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@@ -1512,6 +1512,32 @@ one CPU core and between 512 MB and 1 GB of RAM per running instance.
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Virt-v2v can be run in a virtual machine.
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+=head2 Trimming
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+
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+Virt-v2v attempts to optimize the speed of conversion by ignoring
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+guest filesystem data which is not used. This would include unused
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+filesystem blocks, blocks containing zeroes, and deleted files.
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+
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+To do this, virt-v2v issues a non-destructive L<fstrim(8)> operation.
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+As this happens to an overlay placed over the guest data, it does
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+B<not> affect the source in any way.
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+
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+If this fstrim operation fails, you will see a warning, but virt-v2v
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+will continue anyway. It may run more slowly (in some cases much more
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+slowly), because it is copying the unused parts of the disk.
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+
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+Unfortunately support for fstrim is not universal, and it also depends
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+on specific details of the filesystem, partition alignment, and
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+backing storage. As an example, NTFS filesystems cannot be fstrimmed
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+if they occupy a partition which is not aligned to the underlying
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+storage. That was the default on Windows before Vista. As another
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+example, VFAT filesystems (used by UEFI guests) cannot be trimmed at
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+all.
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+
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+fstrim support in the Linux kernel is improving gradually, so over
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+time some of these restrictions will be lifted and virt-v2v will work
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+faster.
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+
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=head1 POST-CONVERSION TASKS
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=head2 Guest network configuration
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--
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1.8.3.1
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