RE: guaranteed increasing extent allocation

["Rick Smith" <rgsmith72@xxxxxxxxxxx>]

Hello,
	I have made some progress concerning this issue with slight modifications 
to the XFS source code. Specifically, changing the default allocation type 
to XFS_ALLOCTYPE_FIRST_AG and set the default allocation group to zero (when 
nullfb == NULL in xfs_bmap_alloc() in xfs_bmap.c). It is my hope to always 
force allocation to start searching at the beginning of allocation group 0 
and then proceed to the next group once the preceding group is full. Since I 
am using XFS_IOC_RESVSP64 to reserve the files ahead of time, I am not 
concerned with potentially slowing down the file creation process. I also 
realize that this is probably not what most filesystem users are looking 
for, but I think it is crucial for video I/O.
	Is there a way to specify to the allocator to always begin with the start 
of an allocation group? There are cases where a file gets allocated from an 
allocation group and then a later file allocation gets a space closer to the 
beginning of the same allocation group. Is this due to the binary block 
search in xfs_alloc_ag_vextent_size()?
	Also, are there any other potential drawbacks to setting the default 
allocation type to XFS_ALLOCTYPE_FIRST_AG?

Thanks.
Rick Smith

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