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[XFS] Account for inode cluster alignment in all allocations
At ENOSPC, we can get a filesystem shutdown due to a cancelling a dirty transaction in xfs_mkdir or xfs_create. This is due to the initial allocation attempt not taking into account inode alignment and hence we can prepare the AGF freelist for allocation when it's not actually possible to do an allocation. This results in inode allocation returning ENOSPC with a dirty transaction, and hence we shut down the filesystem. Because the first allocation is an exact allocation attempt, we must tell the allocator that the alignment does not affect the allocation attempt. i.e. we will accept any extent alignment as long as the extent starts at the block we want. Unfortunately, this means that if the longest free extent is less than the length + alignment necessary for fallback allocation attempts but is long enough to attempt a non-aligned allocation, we will modify the free list. If we then have the exact allocation fail, all other allocation attempts will also fail due to the alignment constraint being taken into account. Hence the initial attempt needs to set the "alignment slop" field so that alignment, while not required, must be taken into account when determining if there is enough space left in the AG to do the allocation. That means if the exact allocation fails, we will not dirty the freelist if there is not enough space available fo a subsequent allocation to succeed. Hence we get an ENOSPC error back to userspace without shutting down the filesystem. SGI-PV: 978886 SGI-Modid: xfs-linux-melb:xfs-kern:30699a Signed-off-by:David Chinner <dgc@sgi.com> Signed-off-by: