Re: [PATCH 04/17] mount.nfs: /bin/mount already handles --bind & friends

[Chuck Lever <chuck.lever@oracle.com>]

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Neil Brown wrote:
> On Sunday July 15, chuck.lever@oracle.com wrote:
>> Clean-up: remove logic to handle --bind and other such options from
>> mount.nfs[4].
>>
>> These options are already handled in /bin/mount, and the logic for handling
>> them in the NFS helper is currently disabled.  Other helpers such as
>> mount.ocfs2 appear not to support --bind (ie. they rely on /bin/mount to
>> do it).
> 
> Fair enough - I don't suppose the protocol for how /bin/mount talks to
> /sbin/mount.$fstype is documented anywhere???  I guess just in the
> code :-(

There are rumors that somehow the helpers will turn into plug-ins one 
day.  But yes, this is ambiguous and somewhat crappy.  I did ask the 
developers who constructed mount.ocfs2 about this.

>> diff --git a/utils/mount/mount_constants.h b/utils/mount/mount_constants.h
>> index 19a7bf5..3e40841 100644
>> --- a/utils/mount/mount_constants.h
>> +++ b/utils/mount/mount_constants.h
>> @@ -39,6 +39,12 @@ if we have a stack or plain mount - mount atop of it, forming a stack. */
>>  #ifndef MS_VERBOSE
>>  #define MS_VERBOSE	0x8000	/* 32768 */
>>  #endif
>> +
>> +/* Custom mount options for our own purposes.  */
>> +#define MS_DUMMY	0x00000000
>> +#define MS_USERS	0x40000000
>> +#define MS_USER		0x80000000
>> +
>>  /*
>>   * Magic mount flag number. Had to be or-ed to the flag values.
>>   */
> 
> Hmmm.  That wasn't mentioned in the change-log, and I don't find it
> convincing.
> These flags are for internal use in mount.c so it makes lots of sense
> to define them in mount.c so that the definitions never leak.

Well, if we really wanted to be proper about this, we would include the 
mount_constants.c file from utils-linux instead of maintaining a local 
copy.  But since this is a local copy of the header, I figure that 
adding similar local definitions in here is OK.

I'll make a deeper dive on this to see if there's a better way to 
document this.

> Did you have a concrete reason for moving them?

Yes.  See the later patch that moves the mount system call to nfsmount.c 
and nfs4mount.c.  For some reason I don't recall, I thought it would be 
better to move these here in this patch, but that may have been ill-advised.

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