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| /Documentation/filesystems/ext4/ |
| D | blockgroup.rst | 6 The layout of a standard block group is approximately as follows (each
14 - ext4 Super Block
17 - Data Block Bitmap
22 - 1 block
25 - 1 block
26 - 1 block
30 For the special case of block group 0, the first 1024 bytes are unused,
32 The superblock will start at offset 1024 bytes, whichever block that
33 happens to be (usually 0). However, if for some reason the block size =
34 1024, then block 0 is marked in use and the superblock goes in block 1.
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| D | group_descr.rst | 3 Block Group Descriptors
6 Each block group on the filesystem has one of these descriptors
8 descriptors (if present) are the second item in the block group. The
9 standard configuration is for each block group to contain a full copy of
10 the block group descriptor table unless the sparse_super feature flag
14 the inode table (i.e. they can float). This means that within a block
17 property to group several block groups into a flex group and lay out all
21 If the meta_bg feature flag is set, then several block groups are
23 however, the first and last two block groups within the larger meta
30 block group descriptor was only 32 bytes long and therefore ends at
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| D | journal.rst | 45 consumes an entire block group, though mke2fs tries to put it in the
74 or a block revocation list. A finished transaction always ends with a
85 will be an ext4 super block in the usual place, with a matching UUID.
86 The journal superblock will be in the next full block after the
105 Block Header
108 Every block in the journal starts with a common 12-byte header
126 - Description of what this block contains. See the jbd2_blocktype_ table
131 - The transaction ID that goes with this block.
135 The journal block type can be any one of:
144 - Descriptor. This block precedes a series of data blocks that were
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| D | blocks.rst | 6 ext4 allocates storage space in units of “blocks”. A block is a group of
9 block groups. Block size is specified at mkfs time and typically is
10 4KiB. You may experience mounting problems if block size is greater than
14 of structures is stored in terms of the block number the structure lives
43 * - Blocks Per Block Group
48 * - Inodes Per Block Group
53 * - Block Group Size
63 * - Blocks Per File, Block Maps
73 * - File Size, Block Maps
105 * - Blocks Per Block Group
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| D | allocators.rst | 3 Block and Inode Allocation Policy
9 that the head actuator and disk must perform to access a data block,
13 effect of concentrating writes on a single erase block, which can speed
17 The first tool that ext4 uses to combat fragmentation is the multi-block
18 allocator. When a file is first created, the block allocator
23 files) then the file data gets written out in a single multi-block
33 file's data blocks in the same block group as its inode. This cuts down
39 same block group as the directory, when feasible. The working assumption
43 The fifth trick is that the disk volume is cut up into 128MB block
47 the block groups and puts that directory into the least heavily loaded
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| D | bigalloc.rst | 6 At the moment, the default size of a block is 4KiB, which is a commonly
8 ext4 code is not prepared to handle the case where the block size
15 use clustered allocation, so that each bit in the ext4 block allocation
19 This means that each bit in the block allocation bitmap now addresses
20 256 4k blocks. This shrinks the total size of the block allocation
22 means that a block group addresses 32 gigabytes instead of 128 megabytes,
25 The administrator can set a block cluster size at mkfs time (which is
27 on, the block bitmaps track clusters, not individual blocks. This means
28 that block groups can be several gigabytes in size (instead of just
30 block, even for directories. TaoBao had a patchset to extend the “use
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| D | ifork.rst | 8 regular files and directories will use it for file block indexing
15 string is less than 60 bytes long. Otherwise, either extents or block
18 Direct/Indirect Block Addressing
21 In ext2/3, file block numbers were mapped to logical block numbers by
22 means of an (up to) three level 1-1 block map. To find the logical block
23 that stores a particular file block, the code would navigate through
26 block isn't full of garbage.
36 Note that with this block mapping scheme, it is necessary to fill out a
46 In ext4, the file to logical block map has been replaced with an extent
48 requires an indirect block to map all 1,000 entries; with extents, the
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| D | bitmaps.rst | 3 Block and inode Bitmaps
6 The data block bitmap tracks the usage of data blocks within the block
12 block or inode table entry. This implies a block group size of 8 *
15 NOTE: If ``BLOCK_UNINIT`` is set for a given block group, various parts
16 of the kernel and e2fsprogs code pretends that the block bitmap contains
25 Inode tables are statically allocated at mkfs time. Each block group
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| D | directory.rst | 11 such, directory entries are found by reading the data block(s)
22 data blocks and that each block contains a linear array of directory
23 entries. The end of each per-block array is signified by reaching the
24 end of the block; the last entry in the block has a record length that
25 takes it all the way to the end of the block. The end of the entire
116 - Block device file.
150 ``struct ext4_dir_entry`` is placed at the end of each leaf block to
184 - Directory leaf block checksum.
186 The leaf directory block checksum is calculated against the FS UUID, the
188 the entire directory entry block up to (but not including) the fake
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| D | attributes.rst | 7 block on the disk and referenced from inodes via ``inode.i_file_acl*``.
19 where extended attributes can be found is in the block pointed to by
21 block to contain a pointer to a second extended attribute block (or even
23 attribute's value to be stored in a separate data block, though as of
46 The beginning of an extended attribute block is in
76 - Checksum of the extended attribute block.
82 The checksum is calculated against the FS UUID, the 64-bit block number
83 of the extended attribute block, and the entire block (header +
89 long. When stored in an external block, the ``struct ext4_xattr_entry``
113 - Location of this attribute's value on the disk block where it is stored.
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| /Documentation/ABI/stable/ |
| D | sysfs-block | 1 What: /sys/block/<disk>/alignment_offset
5 Storage devices may report a physical block size that is
6 bigger than the logical block size (for instance a drive
13 What: /sys/block/<disk>/discard_alignment
19 the exported logical block size. The discard_alignment
24 What: /sys/block/<disk>/atomic_write_max_bytes
42 What: /sys/block/<disk>/atomic_write_unit_min_bytes
46 [RO] This parameter specifies the smallest block which can
53 What: /sys/block/<disk>/atomic_write_unit_max_bytes
57 [RO] This parameter defines the largest block which can be
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| /Documentation/admin-guide/device-mapper/ |
| D | dm-dust.rst | 15 in the "bad block list" will fail with EIO ("Input/output error").
17 Writes of blocks in the "bad block list will result in the following:
19 1. Remove the block from the "bad block list".
40 Path to the block device.
46 Block size in bytes
59 (For a device with a block size of 512 bytes)
65 (For a device with a block size of 4096 bytes)
73 bad block additions, removals, and remaps will be verbosely logged)::
89 At any time (i.e.: whether the device has the "bad block" emulation
94 kernel: device-mapper: dust: badblock added at block 60
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| D | dm-ebs.rst | 7 a smaller logical block size on a device with a larger logical block
11 Supported emulated logical block sizes 512, 1024, 2048 and 4096.
13 Underlying block size can be set to > 4K to test buffering larger units.
23 Full pathname to the underlying block-device,
29 Number of sectors defining the logical block size to be emulated;
35 Number of sectors defining the logical block size of <dev path>.
37 If not provided, the logical block size of <dev path> will be used.
42 Emulate 1 sector = 512 bytes logical block size on /dev/sda starting at
43 offset 1024 sectors with underlying devices block size automatically set:
47 Emulate 2 sector = 1KiB logical block size on /dev/sda starting at
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| D | dm-zoned.rst | 5 The dm-zoned device mapper target exposes a zoned block device (ZBC and
6 ZAC compliant devices) as a regular block device without any write
8 block device which hides from the user (a file system or an application
9 doing raw block device accesses) the sequential write constraints of
10 host-managed zoned block devices and can mitigate the potential
12 host-aware zoned block devices.
14 For a more detailed description of the zoned block device models and
38 write accesses to the sequential zones of a zoned block device.
40 metadata. It can also use a regular block device together with the zoned
41 block device; in that case the regular block device will be split logically
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| D | vdo-design.rst | 8 compression, zero-block elimination, and thin provisioning. A dm-vdo target
16 Because deduplication rates fall drastically as the block size increases, a
17 vdo target has a maximum block size of 4K. However, it can achieve
18 deduplication rates of 254:1, i.e. up to 254 copies of a given 4K block can
29 duplicate data, and a data store with a reference counted block map that
30 maps from logical block addresses to the actual storage location of the
39 block sizes in order to achieve good deduplication rates, acceptable
80 those savings, vdo does not attempt to find every last duplicate block. It
83 Each block of data is hashed to produce a 16-byte block name. An index
84 record consists of this block name paired with the presumed location of
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| /Documentation/ABI/testing/ |
| D | sysfs-block-loop | 1 What: /sys/block/loopX/loop/autoclear
4 Contact: linux-block@vger.kernel.org
10 What: /sys/block/loopX/loop/backing_file
13 Contact: linux-block@vger.kernel.org
18 What: /sys/block/loopX/loop/offset
21 Contact: linux-block@vger.kernel.org
25 What: /sys/block/loopX/loop/sizelimit
28 Contact: linux-block@vger.kernel.org
30 (RO) The size (in bytes) that the block device maps, starting
33 What: /sys/block/loopX/loop/partscan
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| D | sysfs-block-zram | 1 What: /sys/block/zram<id>/disksize
10 What: /sys/block/zram<id>/initstate
17 What: /sys/block/zram<id>/reset
25 What: /sys/block/zram<id>/max_comp_streams
33 What: /sys/block/zram<id>/comp_algorithm
41 What: /sys/block/zram<id>/mem_used_max
51 What: /sys/block/zram<id>/mem_limit
60 What: /sys/block/zram<id>/compact
68 What: /sys/block/zram<id>/io_stat
73 statistics not accounted by block layer. For example,
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| D | sysfs-block-bcache | 1 What: /sys/block/<disk>/bcache/unregister
11 What: /sys/block/<disk>/bcache/clear_stats
17 What: /sys/block/<disk>/bcache/cache
24 What: /sys/block/<disk>/bcache/cache_hits
31 What: /sys/block/<disk>/bcache/cache_misses
37 What: /sys/block/<disk>/bcache/cache_hit_ratio
43 What: /sys/block/<disk>/bcache/sequential_cutoff
51 What: /sys/block/<disk>/bcache/bypassed
59 What: /sys/block/<disk>/bcache/writeback
68 What: /sys/block/<disk>/bcache/writeback_running
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| /Documentation/admin-guide/blockdev/ |
| D | zram.rst | 2 zram: Compressed RAM-based block devices
8 The zram module creates RAM-based block devices named /dev/zram<id>
15 /sys/block/zram<id>/
57 echo 3 > /sys/block/zram0/max_comp_streams
88 cat /sys/block/zram0/max_comp_streams
101 cat /sys/block/zram0/comp_algorithm
105 echo lzo > /sys/block/zram0/comp_algorithm
124 echo "algo=zstd dict=/etc/dictioary" > /sys/block/zram0/algorithm_params
128 /sys/block/zram0/algorithm_params
132 /sys/block/zram0/algorithm_params
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| /Documentation/userspace-api/media/v4l/ |
| D | dev-rds.rst | 101 - Least Significant Byte of RDS Block
104 - Most Significant Byte of RDS Block
106 - ``block``
107 - Block description
110 .. _v4l2-rds-block:
114 .. flat-table:: Block description
120 - Block (aka offset) of the received data.
126 block.
129 reception of this block.
132 .. _v4l2-rds-block-codes:
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| /Documentation/devicetree/bindings/powerpc/fsl/ |
| D | mpic-msgr.txt | 10 block. The type shall be <string-list> and the value shall be of the form
15 message register block's addressable register space. The type shall be
25 - mpic-msgr-receive-mask: Specifies what registers in the containing block
29 be <u32>. If not present, then all of the message registers in the block
34 An alias should be created for every message register block. They are not
37 'mpic-msgr-block<n>', where <n> is an integer specifying the block's number.
47 mpic_msgr_block0: mpic-msgr-block@41400 {
50 // Message registers 0 and 2 in this block can receive interrupts on
56 mpic_msgr_block1: mpic-msgr-block@42400 {
59 // Message registers 0 and 2 in this block can receive interrupts on
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| /Documentation/filesystems/ |
| D | sysv-fs.rst | 52 * Size of a block or zone (data allocation unit on disk)
59 * General layout: all have one boot block, one super block and
62 all the block numbers (including the super block) are offset by one track.
103 There is a cache of a certain number of free inodes in the super-block.
106 * Free block management:
112 since it is not true that every free block contains a pointer to
113 the next free block. Rather, the free blocks are organized in chunks
114 of limited size, and every now and then a free block contains pointers
116 contains pointers and so on. The list terminates with a "block number"
117 0 on Xenix FS and SystemV FS, with a block zeroed out on Coherent FS.
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| /Documentation/block/ |
| D | blk-mq.rst | 4 Multi-Queue Block IO Queueing Mechanism (blk-mq)
7 The Multi-Queue Block IO Queueing Mechanism is an API to enable fast storage
9 through queueing and submitting IO requests to block devices simultaneously,
19 development of the kernel. The Block IO subsystem aimed to achieve the best
32 The former design had a single queue to store block IO requests with a single
36 to different CPUs) wanted to perform block IO. Instead of this, the blk-mq API
44 When the userspace performs IO to a block device (reading or writing a file,
46 the block device, acting as middleware between the userspace (and a file
47 system, if present) and the block device driver.
50 queues. When the request arrives at the block layer, it will try the shortest
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| D | switching-sched.rst | 9 /sys/block/<device>/queue/iosched
16 It is possible to change the IO scheduler for a given block device on
22 echo SCHEDNAME > /sys/block/DEV/queue/scheduler
28 a "cat /sys/block/DEV/queue/scheduler" - the list of valid names
31 # cat /sys/block/sda/queue/scheduler
33 # echo none >/sys/block/sda/queue/scheduler
34 # cat /sys/block/sda/queue/scheduler
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| /Documentation/devicetree/bindings/dma/ |
| D | fsl-qdma.yaml | 27 - description: Block regs
52 block-number:
54 description: the virtual block number
56 block-offset:
58 description: the offset of different virtual block
62 description: status queue size of per virtual block
67 command queue size of per virtual block, the size number
83 - block-number
84 - block-offset
121 <0x838a000 0x2000>; /* Block regs */
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