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Re: [libvirt] [PATCH 6/8] qemuDomainCreateDeviceRecursive: Support file mount points




On 07/10/2017 09:33 AM, Michal Privoznik wrote:
> On 06/28/2017 12:11 AM, John Ferlan wrote:
>>
>>
>> On 06/22/2017 12:18 PM, Michal Privoznik wrote:
>>> https://bugzilla.redhat.com/show_bug.cgi?id=1462060
>>>
>>> When building a qemu namespace we might be dealing with bare
>>> regular files. Files that live under /dev. For instance
>>> /dev/my_awesome_disk:
>>>
>>>   <disk type='file' device='disk'>
>>>     <driver name='qemu' type='qcow2'/>
>>>     <source file='/dev/my_awesome_disk'/>
>>>     <target dev='vdc' bus='virtio'/>
>>>   </disk>
>>>
>>>   # qemu-img create -f qcow2 /dev/my_awesome_disk 10M
>>>
>>> So far we were mknod()-ing them which is
>>> obviously wrong. We need to touch the file and bind mount it to
>>> the original:
>>>
>>> 1) touch /var/run/libvirt/qemu/fedora.dev/my_awesome_disk
>>> 2) mount --bind /dev/my_awesome_disk /var/run/libvirt/qemu/fedora.dev/my_awesome_disk
>>>
>>> Later, when the new /dev is built and replaces original /dev the
>>> file is going to live at expected location.
>>>
>>> Signed-off-by: Michal Privoznik <mprivozn redhat com>
>>> ---
>>>  src/qemu/qemu_domain.c | 28 ++++++++++++++++++++--------
>>>  1 file changed, 20 insertions(+), 8 deletions(-)
>>>
>>> diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c
>>> index 977b5c089..6d7c218a2 100644
>>> --- a/src/qemu/qemu_domain.c
>>> +++ b/src/qemu/qemu_domain.c
>>> @@ -7708,6 +7708,7 @@ qemuDomainCreateDeviceRecursive(const char *device,
>>>      int ret = -1;
>>>      bool isLink = false;
>>>      bool isDev = false;
>>> +    bool isReg = false;
>>>      bool create = false;
>>>  #ifdef WITH_SELINUX
>>>      char *tcon = NULL;
>>> @@ -7731,6 +7732,7 @@ qemuDomainCreateDeviceRecursive(const char *device,
>>>  
>>>      isLink = S_ISLNK(sb.st_mode);
>>>      isDev = S_ISCHR(sb.st_mode) || S_ISBLK(sb.st_mode);
>>> +    isReg = S_ISREG(sb.st_mode);
>>>  
>>>      /* Here, @device might be whatever path in the system. We
>>>       * should create the path in the namespace iff it's "/dev"
>>> @@ -7842,16 +7844,12 @@ qemuDomainCreateDeviceRecursive(const char *device,
>>>              }
>>>              goto cleanup;
>>>          }
>>> -
>>> -        /* Set the file permissions again: mknod() is affected by the
>>> -         * current umask, and as such might not have set them correctly */
>>> +    } else if (isReg) {
>>>          if (create &&
>>> -            chmod(devicePath, sb.st_mode) < 0) {
>>> -            virReportSystemError(errno,
>>> -                                 _("Failed to set permissions for device %s"),
>>> -                                 devicePath);
>>> +            virFileTouch(devicePath, sb.st_mode) < 0)
>>>              goto cleanup;
>>> -        }
>>> +        /* Just create the file here so that code below sets
>>> +         * proper owner and mode. Bind mount only after that. */
>>>      } else {
>>>          virReportError(VIR_ERR_OPERATION_UNSUPPORTED,
>>>                         _("unsupported device type %s %o"),
>>> @@ -7871,6 +7869,15 @@ qemuDomainCreateDeviceRecursive(const char *device,
>>>          goto cleanup;
>>>      }
>>
>>
>>> +    /* Symlinks don't have mode */
>>> +    if (!isLink &&
>>
>>
>> So the "one" concern I have would be to use (isDev || isReg) instead of
>> (!isLink) - if only to CYA that something new bool isn't invented that
>> would also not need the chmod.  IDC, I'm fine with it this way - your
>> call - just figured I'd point it out.
> 
> Funny, I didn't want to use isDev || isReg for exactly this reason. When
> new type is introduced nothing needs to be adjusted here. The new type
> is more likely to support mode - frankly so far symlinks are the only
> type that I've met that doesn't have mode. Therefore I'd like to keep as is.
> 

That's fine - I was 50/50 anyway...

John

>>
>> Reviewed-by: John Ferlan <jferlan redhat com>
> 
> Thanks.
> 
> Michal
> 


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