File Systems: Difference between revisions

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Revision as of 06:16, 2 November 2023 view source osdev>Moltony112 m Add btrfs into expert filesystems section ← Older edit		Latest revision as of 15:28, 29 May 2024 view source osdev>Drkeph Undo revision 28897 by Drkeph (talk) duplicate line removed
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Line 81: '''[[USTAR]]''' * <code>+</code> Of these beginner "filesystems", this is the simplest by far to implement * <code>+</code> Uses 512 byte sectors, just like floppies and disks * <code>+</code> Incredibly simple: a sector with metadata followed by data sectors * <code>+</code> Widely used: ~~a utility~~utilities to create tar images are available for every mainstream OS and many minor ones * <code>+</code> Supports special files (like devices and symlinks) * <code>+</code> Supports Unix permissions Line 129 ⟶ 128: '''[[ISO 9660]]''' The defined standard for CDs. If you boot from CD then this is the way to go. If not, don't make it your first filesystem. '''[[PureFS]]''' * <code>+</code> Easy to implement * <code>+</code> Supports large files * <code>+</code> Supports nested directories * <code>-</code> No support for Unix permissions * <code>-</code> It can be journalable, provided that the OS takes care of this task itself * <code>-</code> The maximum length of the file name is 255 characters * <code>-</code> The maximum number of volumes is 40 * <code>-</code> Does not support Unicode names * <code>-</code> Takes up a lot of space === Rolling your own === Line 138 ⟶ 148: * Consider carefully what it will be used for. * Use a program to figure out the layout (e.g. a spreadsheet). The basic areas needed are: Bootsector. This is essential for booting on some systems such as BIOS-x86 and Atari ST, unnecessary for others such as UEFI and OpenFirmware. Even if you don't intend to boot on systems which require it, reserving the first sector will allow your OS to be ported to them at a later time. Note that reserving space for a MBR-like partition table is needed to allow the filesystem to work in "logical partitions". Bootsector. Unless you are booting with UEFI, this is a must. Even then, it's recommended to include it in the specs for compatibility with older file systems. This section should contain at a minimum the disk size, location of the file table, hidden sectors for multiple partition disks, and a version number. I'd be leaving plenty of reserved space for features you don't think of. Don't forget to leave space for a jmp instruction and the boot code!. ** Partition metadata. This could fit into the first sector with the boot code, or be a separate group of sectors at a specific location. (FAT puts it in the first sector, calling it the FAT parameter block. ext* use a separate location, calling it the superblock.) At a minimum, this should contain the filesystem size, location of the file table, and a version number. Leave plenty of reserved space for features you don't think of. If you put it in the first sector, don't forget to leave space for a jmp instruction, the boot code, and a partition table! File table. Don't think of this as just a simple table containing a list of files and their locations. One idea is, instead of storing files, the system would store file parts, and the file table would list the parts in each file. This would be useful for saving space if many files on the disk are the same or similar (for example, license agreements). Data area. Files will be stored here.