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Re: [libvirt] [PATCH 2/8] qemuDomainBuildNamespace: Handle special file mount points



On 06/27/2017 11:37 PM, John Ferlan wrote:
> 
> 
> On 06/22/2017 12:18 PM, Michal Privoznik wrote:
>> https://bugzilla.redhat.com/show_bug.cgi?id=1459592
>>
>> In 290a00e41d I've tried to fix the process of building a
>> qemu namespace when dealing with file mount points. What I
>> haven't realized then is that we might be dealing not with just
>> regular files but also special files (like sockets). Indeed, try
>> the following:
>>
>> 1) socat unix-listen:/tmp/soket stdio
>> 2) touch /dev/socket
>> 3) mount --bind /tmp/socket /dev/socket
>> 4) virsh start anyDomain
>>
>> Problem with my previous approach is that I wasn't creating the
>> temporary location (where mount points under /dev are moved) for
>> anything but directories and regular files.
>>
>> Signed-off-by: Michal Privoznik <mprivozn redhat com>
>> ---
>>  src/qemu/qemu_domain.c | 6 ++++--
>>  1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c
>> index 8e7404da6..212717c80 100644
>> --- a/src/qemu/qemu_domain.c
>> +++ b/src/qemu/qemu_domain.c
>> @@ -8356,9 +8356,11 @@ qemuDomainBuildNamespace(virQEMUDriverConfigPtr cfg,
>>              goto cleanup;
>>          }
>>  
>> -        /* At this point, devMountsPath is either a regular file or a directory. */
>> +        /* At this point, devMountsPath is either:
>> +         * a file (regular or special), or
>> +         * a directory. */
>>          if ((S_ISDIR(sb.st_mode) && virFileMakePath(devMountsSavePath[i]) < 0) ||
>> -            (S_ISREG(sb.st_mode) && virFileTouch(devMountsSavePath[i], sb.st_mode) < 0)) {
>> +            (!S_ISDIR(sb.st_mode) && virFileTouch(devMountsSavePath[i], sb.st_mode) < 0)) {
> 
> It would seem to me that this would open Pandora's box to all different
> types of things (BLK, CHR, FIFO, LNK, NAM, MPB, MPC, NWK) - some of
> which it may not be so popular to perform a touch on.
> 
> I think you should keep it specific...  Perhaps use the list from
> qemuDomainCreateDeviceRecursive:
> 
>    isReg = S_ISREG(sb.st_mode) || S_ISFIFO(sb.st_mode) ||
> S_ISSOCK(sb.st_mode);

Not really. mount --bind makes the target to be the correct type. IOW:

# create a regular file
touch /tmp/blah

# here, assume /source/socket is a socket
mount --bind /source/socket /tmp/blah

# now, /tmp/blah will be type of socket too

The only problem here is that for file based 'devices' (or things in
general) we have to create the file whereas for directories we have to
create directories. Just like in the example.

BTW, what type of file are NAM, MPB, MPC, NWK?

Michal


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