The first block in any Ext2 partition is never managed by the Ext2 filesystem, since it is reserved for the partition boot sector (see Appendix A). The rest of the Ext2 partition is split into block groups, each of which has the layout shown in Figure 17-1. As you will notice from the figure, some data structures must fit in exactly one block, while others may require more than one block. All the block groups in the filesystem have the same size and are stored sequentially, thus the kernel can derive the location of a block group in a disk simply from its integer index. more...
Traditionally, Unix/Linux/POSIX filenames can be almost any sequence of bytes, and their meaning is unassigned. The only real rules are that "/" is always the directory separator, and that filenames can't contain byte 0 (because this is the terminator). Although this is flexible, this creates many unnecessary problems. In particular, this lack of limitations makes it unnecessarily difficult to write correct programs (enabling many security flaws), makes it impossible to consistently and accurately display filenames, causes portability problems, and confuses users. more ....
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