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Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel…
…/git/viro/vfs Pull vfs pile 1 from Al Viro: "This is _not_ all; in particular, Miklos' and Jan's stuff is not there yet." * 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: (64 commits) ext4: initialization of ext4_li_mtx needs to be done earlier debugfs-related mode_t whack-a-mole hfsplus: add an ioctl to bless files hfsplus: change finder_info to u32 hfsplus: initialise userflags qnx4: new helper - try_extent() qnx4: get rid of qnx4_bread/qnx4_getblk take removal of PF_FORKNOEXEC to flush_old_exec() trim includes in inode.c um: uml_dup_mmap() relies on ->mmap_sem being held, but activate_mm() doesn't hold it um: embed ->stub_pages[] into mmu_context gadgetfs: list_for_each_safe() misuse ocfs2: fix leaks on failure exits in module_init ecryptfs: make register_filesystem() the last potential failure exit ntfs: forgets to unregister sysctls on register_filesystem() failure logfs: missing cleanup on register_filesystem() failure jfs: mising cleanup on register_filesystem() failure make configfs_pin_fs() return root dentry on success configfs: configfs_create_dir() has parent dentry in dentry->d_parent configfs: sanitize configfs_create() ...
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The QNX6 Filesystem | ||
=================== | ||
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The qnx6fs is used by newer QNX operating system versions. (e.g. Neutrino) | ||
It got introduced in QNX 6.4.0 and is used default since 6.4.1. | ||
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Option | ||
====== | ||
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mmi_fs Mount filesystem as used for example by Audi MMI 3G system | ||
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Specification | ||
============= | ||
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qnx6fs shares many properties with traditional Unix filesystems. It has the | ||
concepts of blocks, inodes and directories. | ||
On QNX it is possible to create little endian and big endian qnx6 filesystems. | ||
This feature makes it possible to create and use a different endianness fs | ||
for the target (QNX is used on quite a range of embedded systems) plattform | ||
running on a different endianess. | ||
The Linux driver handles endianness transparently. (LE and BE) | ||
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Blocks | ||
------ | ||
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The space in the device or file is split up into blocks. These are a fixed | ||
size of 512, 1024, 2048 or 4096, which is decided when the filesystem is | ||
created. | ||
Blockpointers are 32bit, so the maximum space that can be adressed is | ||
2^32 * 4096 bytes or 16TB | ||
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The superblocks | ||
--------------- | ||
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The superblock contains all global information about the filesystem. | ||
Each qnx6fs got two superblocks, each one having a 64bit serial number. | ||
That serial number is used to identify the "active" superblock. | ||
In write mode with reach new snapshot (after each synchronous write), the | ||
serial of the new master superblock is increased (old superblock serial + 1) | ||
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So basically the snapshot functionality is realized by an atomic final | ||
update of the serial number. Before updating that serial, all modifications | ||
are done by copying all modified blocks during that specific write request | ||
(or period) and building up a new (stable) filesystem structure under the | ||
inactive superblock. | ||
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Each superblock holds a set of root inodes for the different filesystem | ||
parts. (Inode, Bitmap and Longfilenames) | ||
Each of these root nodes holds information like total size of the stored | ||
data and the adressing levels in that specific tree. | ||
If the level value is 0, up to 16 direct blocks can be adressed by each | ||
node. | ||
Level 1 adds an additional indirect adressing level where each indirect | ||
adressing block holds up to blocksize / 4 bytes pointers to data blocks. | ||
Level 2 adds an additional indirect adressig block level (so, already up | ||
to 16 * 256 * 256 = 1048576 blocks that can be adressed by such a tree)a | ||
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Unused block pointers are always set to ~0 - regardless of root node, | ||
indirect adressing blocks or inodes. | ||
Data leaves are always on the lowest level. So no data is stored on upper | ||
tree levels. | ||
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The first Superblock is located at 0x2000. (0x2000 is the bootblock size) | ||
The Audi MMI 3G first superblock directly starts at byte 0. | ||
Second superblock position can either be calculated from the superblock | ||
information (total number of filesystem blocks) or by taking the highest | ||
device address, zeroing the last 3 bytes and then substracting 0x1000 from | ||
that address. | ||
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0x1000 is the size reserved for each superblock - regardless of the | ||
blocksize of the filesystem. | ||
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Inodes | ||
------ | ||
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Each object in the filesystem is represented by an inode. (index node) | ||
The inode structure contains pointers to the filesystem blocks which contain | ||
the data held in the object and all of the metadata about an object except | ||
its longname. (filenames longer than 27 characters) | ||
The metadata about an object includes the permissions, owner, group, flags, | ||
size, number of blocks used, access time, change time and modification time. | ||
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Object mode field is POSIX format. (which makes things easier) | ||
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There are also pointers to the first 16 blocks, if the object data can be | ||
adressed with 16 direct blocks. | ||
For more than 16 blocks an indirect adressing in form of another tree is | ||
used. (scheme is the same as the one used for the superblock root nodes) | ||
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The filesize is stored 64bit. Inode counting starts with 1. (whilst long | ||
filename inodes start with 0) | ||
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Directories | ||
----------- | ||
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A directory is a filesystem object and has an inode just like a file. | ||
It is a specially formatted file containing records which associate each | ||
name with an inode number. | ||
'.' inode number points to the directory inode | ||
'..' inode number points to the parent directory inode | ||
Eeach filename record additionally got a filename length field. | ||
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One special case are long filenames or subdirectory names. | ||
These got set a filename length field of 0xff in the corresponding directory | ||
record plus the longfile inode number also stored in that record. | ||
With that longfilename inode number, the longfilename tree can be walked | ||
starting with the superblock longfilename root node pointers. | ||
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Special files | ||
------------- | ||
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Symbolic links are also filesystem objects with inodes. They got a specific | ||
bit in the inode mode field identifying them as symbolic link. | ||
The directory entry file inode pointer points to the target file inode. | ||
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Hard links got an inode, a directory entry, but a specific mode bit set, | ||
no block pointers and the directory file record pointing to the target file | ||
inode. | ||
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Character and block special devices do not exist in QNX as those files | ||
are handled by the QNX kernel/drivers and created in /dev independant of the | ||
underlaying filesystem. | ||
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Long filenames | ||
-------------- | ||
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Long filenames are stored in a seperate adressing tree. The staring point | ||
is the longfilename root node in the active superblock. | ||
Each data block (tree leaves) holds one long filename. That filename is | ||
limited to 510 bytes. The first two starting bytes are used as length field | ||
for the actual filename. | ||
If that structure shall fit for all allowed blocksizes, it is clear why there | ||
is a limit of 510 bytes for the actual filename stored. | ||
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Bitmap | ||
------ | ||
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The qnx6fs filesystem allocation bitmap is stored in a tree under bitmap | ||
root node in the superblock and each bit in the bitmap represents one | ||
filesystem block. | ||
The first block is block 0, which starts 0x1000 after superblock start. | ||
So for a normal qnx6fs 0x3000 (bootblock + superblock) is the physical | ||
address at which block 0 is located. | ||
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Bits at the end of the last bitmap block are set to 1, if the device is | ||
smaller than addressing space in the bitmap. | ||
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Bitmap system area | ||
------------------ | ||
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The bitmap itself is devided into three parts. | ||
First the system area, that is split into two halfs. | ||
Then userspace. | ||
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The requirement for a static, fixed preallocated system area comes from how | ||
qnx6fs deals with writes. | ||
Each superblock got it's own half of the system area. So superblock #1 | ||
always uses blocks from the lower half whilst superblock #2 just writes to | ||
blocks represented by the upper half bitmap system area bits. | ||
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Bitmap blocks, Inode blocks and indirect addressing blocks for those two | ||
tree structures are treated as system blocks. | ||
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The rational behind that is that a write request can work on a new snapshot | ||
(system area of the inactive - resp. lower serial numbered superblock) while | ||
at the same time there is still a complete stable filesystem structer in the | ||
other half of the system area. | ||
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When finished with writing (a sync write is completed, the maximum sync leap | ||
time or a filesystem sync is requested), serial of the previously inactive | ||
superblock atomically is increased and the fs switches over to that - then | ||
stable declared - superblock. | ||
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For all data outside the system area, blocks are just copied while writing. |
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Original file line number | Diff line number | Diff line change |
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@@ -218,6 +218,7 @@ Code Seq#(hex) Include File Comments | |
'h' 00-7F conflict! Charon filesystem | ||
<mailto:[email protected]> | ||
'h' 00-1F linux/hpet.h conflict! | ||
'h' 80-8F fs/hfsplus/ioctl.c | ||
'i' 00-3F linux/i2o-dev.h conflict! | ||
'i' 0B-1F linux/ipmi.h conflict! | ||
'i' 80-8F linux/i8k.h | ||
|
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