Re: [PATCH v2 1/2] lxc: Assign aliases to filesystem devices

17 Jun 2026

On 6/12/26 07:14, Radosław Śmigielski via Devel wrote:
...
From: Radoslaw Smigielski <rsmigiel@redhat.com>
LXC domains did not assign device aliases to filesystem devices
during domain startup. Only console devices received aliases.
This change assigns aliases in the format 'fs0', 'fs1', etc. to all
filesystem devices during domain startup, following the same pattern
used for console devices.
Before this patch, virsh dumpxml showed filesystem devices without aliases:
<filesystem type='mount' accessmode='passthrough'>
      <source dir='/var/lib/libvirt/lxc/demo-root'/>
      <target dir='/'/>
    </filesystem>
    <filesystem type='file' accessmode='passthrough'>
      <driver type='loop' format='raw'/>
      <source file='/var/tmp/short6.raw'/>
      <target dir='/short6'/>
    </filesystem>
    <console type='pty' tty='/dev/pts/8'>
      <source path='/dev/pts/8'/>
      <target type='lxc' port='0'/>
      <alias name='console0'/>    
    </console>
After this patch, filesystem devices have auto-generated aliases:
<filesystem type='mount' accessmode='passthrough'>
      <source dir='/var/lib/libvirt/lxc/demo-root'/>
      <target dir='/'/>
      <alias name='fs0'/>          
    </filesystem>
    <filesystem type='file' accessmode='passthrough'>
      <driver type='loop' format='raw'/>
      <source file='/var/tmp/short6.raw'/>
      <target dir='/short6'/>
      <alias name='fs1'/>          
    </filesystem>
    <console type='pty' tty='/dev/pts/8'>
      <source path='/dev/pts/8'/>
      <target type='lxc' port='0'/>
      <alias name='console0'/>
    </console>
This is a prerequisite for fixing bug #63 (loop device path length
limitation), where filesystem device aliases will be used to compose
synthetic lo_file_name references in the format "libvirt-$UUID-$DEVALIAS".
Related: https://gitlab.com/libvirt/libvirt/-/work_items/63
Signed-off-by: Radoslaw Smigielski <rsmigiel@redhat.com>
---
 src/lxc/lxc_process.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/lxc/lxc_process.c b/src/lxc/lxc_process.c
index 2c0bcb9dd3aa..aae9fcc9dfd1 100644
--- a/src/lxc/lxc_process.c
+++ b/src/lxc/lxc_process.c
@@ -1350,6 +1350,12 @@ int virLXCProcessStart(virLXCDriver * driver,
         vm->def->consoles[i]->info.alias = g_strdup_printf("console%zu", i);
     }
+    VIR_DEBUG("Setting up filesystem aliases");
+    for (i = 0; i < vm->def->nfss; i++) {
+        g_free(vm->def->fss[i]->info.alias);
I don't think this g_free() is necessary. I know you took inspiration
from a couple of lines above but I find it pointless there too. I mean,
every domain starts with no aliases (in its inactive state). Then this
function calls the following at its beginning:

    if (virDomainObjSetDefTransient(driver->xmlopt, vm, NULL) < 0)
        goto cleanup;

which copies inactive domain definition (i.e. XML parser skips aliases
intentionally) into vm->newDef. So later when domain is shutoff,
virDomainObjRemoveTransientDef() is called which throws away vm->def and
restores the original definition (without aliases) from vm->newDef.

I can remove it before merging, if you want to merge just this one. I
worry that 2/2 is a bit more complicated.
...
+        vm->def->fss[i]->info.alias = g_strdup_printf("fs%zu", i);
+    }
+
     VIR_DEBUG("Setting up Interfaces");
     if (virLXCProcessSetupInterfaces(driver, vm->def, &veths) < 0)
         goto cleanup;
Michal

    

Re: [PATCH v2 1/2] lxc: Assign aliases to filesystem devices

Michal Prívozník