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From 6c4c780eda082ef395b70af89b8b8942b9ad4a9d Mon Sep 17 00:00:00 2001
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Message-Id: <6c4c780eda082ef395b70af89b8b8942b9ad4a9d@dist-git>
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From: Michal Privoznik <mprivozn@redhat.com>
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Date: Mon, 8 Jan 2018 10:16:19 +0100
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Subject: [PATCH] qemuDomainAttachDeviceMknodHelper: Remove symlink before
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creating it
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https://bugzilla.redhat.com/show_bug.cgi?id=1528502
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So imagine you have /dev/blah symlink which points to /dev/sda.
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You attach /dev/blah as disk to your domain. Libvirt correctly
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creates the /dev/blah -> /dev/sda symlink in the qemu namespace.
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However, then you detach the disk, change the symlink so that it
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points to /dev/sdb and tries to attach the disk again. This time,
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however, the attach fails (well, qemu attaches wrong disk)
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because the code assumes that symlinks don't change. Well they
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do.
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This is inspired by test fix written by Eduardo Habkost.
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Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
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Reviewed-by: Andrea Bolognani <abologna@redhat.com>
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(cherry picked from commit db98e7f67ea0d7699410f514f01947cef5128a6c)
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Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
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Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
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Reviewed-by: Andrea Bolognani <abologna@redhat.com>
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---
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src/qemu/qemu_domain.c | 22 ++++++++++++++++------
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1 file changed, 16 insertions(+), 6 deletions(-)
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diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c
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index 8967f2774d..b0c78cc7c4 100644
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--- a/src/qemu/qemu_domain.c
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+++ b/src/qemu/qemu_domain.c
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@@ -9559,13 +9559,23 @@ qemuDomainAttachDeviceMknodHelper(pid_t pid ATTRIBUTE_UNUSED,
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if (isLink) {
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VIR_DEBUG("Creating symlink %s -> %s", data->file, data->target);
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+
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+ /* First, unlink the symlink target. Symlinks change and
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+ * therefore we have no guarantees that pre-existing
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+ * symlink is still valid. */
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+ if (unlink(data->file) < 0 &&
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+ errno != ENOENT) {
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+ virReportSystemError(errno,
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+ _("Unable to remove symlink %s"),
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+ data->file);
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+ goto cleanup;
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+ }
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+
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if (symlink(data->target, data->file) < 0) {
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- if (errno != EEXIST) {
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- virReportSystemError(errno,
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- _("Unable to create symlink %s"),
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- data->target);
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- goto cleanup;
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- }
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+ virReportSystemError(errno,
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+ _("Unable to create symlink %s (pointing to %s)"),
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+ data->file, data->target);
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+ goto cleanup;
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} else {
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delDevice = true;
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}
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--
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2.15.1
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