/* * Select the desired position for the next block in a file. The file is * logically divided into sections. The first section is composed of the * direct blocks. Each additional section contains fs_maxbpg blocks. * * If no blocks have been allocated in the first section, the policy is to * request a block in the same cylinder group as the inode that describes * the file. If no blocks have been allocated in any other section, the * policy is to place the section in a cylinder group with a greater than * average number of free blocks. An appropriate cylinder group is found * by using a rotor that sweeps the cylinder groups. When a new group of * blocks is needed, the sweep begins in the cylinder group following the * cylinder group from which the previous allocation was made. The sweep * continues until a cylinder group with greater than the average number * of free blocks is found. If the allocation is for the first block in an * indirect block, the information on the previous allocation is unavailable; * here a best guess is made based upon the logical block number being * allocated. * * If a section is already partially allocated, the policy is to * contiguously allocate fs_maxcontig blocks. The end of one of these * contiguous blocks and the beginning of the next is laid out * contigously if possible. * * => um_lock held on entry and exit */