[pve-devel] [PATCH common v4 2/2] sysfstools: fix regression on binding to vfio-pci

[Dominik Csapak <d.csapak@proxmox.com>]

when starting a vm with passthrough, we have to bind all normal pci
devices to vfio-pci. This happens by

* unbinding from current driver
* telling vfio-pci the 'vendorid modelid' combo so it knows this device
  class can use the driver (by writing to 'new_id')
* actually binding the device to vfio-pci

if there are multiple devices of the same 'vendorid modelid' class on
the host (and passed through), only the first write to 'new_id' is
successful, all subsequent ones return EEXIST.

This could happen e.g. for setups with multiple GPUs that have the same
audio chip.

To fix this, ignore the EEXIST error for this write to new_id, by adding
a new parameter to file_write for this.

If we need to ignore other errors in the future, we can still make this
more generic.

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
---
changes from v3:
* add ignoring to file_write in this patch
* only add a single option for ignoring EEXIST, we can add more/make it
  more generic later too if we need it.


 src/PVE/SysFSTools.pm | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/src/PVE/SysFSTools.pm b/src/PVE/SysFSTools.pm
index 772f6d6..8f39da3 100644
--- a/src/PVE/SysFSTools.pm
+++ b/src/PVE/SysFSTools.pm
@@ -4,6 +4,7 @@ use strict;
 use warnings;
 
 use IO::File;
+use POSIX qw(EEXIST);
 
 use PVE::Tools qw(file_read_firstline dir_glob_foreach);
 
@@ -212,8 +213,9 @@ sub check_iommu_support{
 }
 
 # writes $buf into $filename, on success returns 1, on error returns 0 and warns
+# if $allow_existing is set, an EEXIST error will be handled as success
 sub file_write {
-    my ($filename, $buf) = @_;
+    my ($filename, $buf, $allow_existing) = @_;
 
     my $fh = IO::File->new($filename, "w");
     return undef if !$fh;
@@ -224,6 +226,7 @@ sub file_write {
     if (defined($res)) {
 	return 1;
     } elsif (my $err = $!) {
+	return 1 if $allow_existing && $err == EEXIST;
 	warn "error writing '$buf' to '$filename': $err\n";
     }
 
@@ -309,7 +312,8 @@ sub pci_dev_bind_to_vfio {
     return 1 if -d $testdir;
 
     my $data = "$dev->{vendor} $dev->{device}";
-    return undef if !file_write("$vfio_basedir/new_id", $data);
+    # allow EEXIST for multiple devices with the same vendor/modelid
+    return undef if !file_write("$vfio_basedir/new_id", $data, 1);
 
     my $fn = "$pcisysfs/devices/$name/driver/unbind";
     if (!file_write($fn, $name)) {
-- 
2.39.5



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