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| /Documentation/filesystems/nfs/ |
| D | Exporting | 8 All filesystem operations require a dentry (or two) as a starting
9 point. Local applications have a reference-counted hold on suitable
11 applications that access a filesystem via a remote filesystem protocol
12 such as NFS may not be able to hold such a reference, and so need a
13 different way to refer to a particular dentry. As the alternative
22 This byte string will be called a "filehandle fragment" as it
33 The dcache normally contains a proper prefix of any given filesystem
37 maintained easily (by each object maintaining a reference count on
40 However when objects are included into the dcache by interpreting a
41 filehandle fragment, there is no automatic creation of a path prefix
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| D | rpc-cache.txt | 1 This document gives a brief introduction to the caching
8 a wide variety of values to be caches.
10 There are a number of caches that are similar in structure though
11 quite possibly very different in content and use. There is a corpus
35 Creating a Cache
38 1/ A cache needs a datum to store. This is in the form of a
39 structure definition that must contain a
42 It will also contain a key and some content.
45 2/ A cache needs a "cache_detail" structure that
52 a pointer to the cache_detail embedded within the
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| /Documentation/ABI/testing/ |
| D | sysfs-bus-rpmsg | 6 Every rpmsg device is a communication channel with a remote
7 processor. Channels are identified with a (textual) name,
18 Every rpmsg device is a communication channel with a remote
19 processor. Channels have a local ("source") rpmsg address,
21 starts listening on one end of a channel, it assigns it with
22 a unique rpmsg address (a 32 bits integer). This way when
24 dispatches them to the listening entity (a kernel driver).
36 Every rpmsg device is a communication channel with a remote
37 processor. Channels have a local ("source") rpmsg address,
39 starts listening on one end of a channel, it assigns it with
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| /Documentation/ |
| D | kobject.txt | 13 place. Dealing with kobjects requires understanding a few different types,
15 easier, we'll take a multi-pass approach, starting with vague terms and
19 - A kobject is an object of type struct kobject. Kobjects have a name
20 and a reference count. A kobject also has a parent pointer (allowing
21 objects to be arranged into hierarchies), a specific type, and,
22 usually, a representation in the sysfs virtual filesystem.
32 - A ktype is the type of object that embeds a kobject. Every structure
33 that embeds a kobject needs a corresponding ktype. The ktype controls
36 - A kset is a group of kobjects. These kobjects can be of the same ktype
42 When you see a sysfs directory full of other directories, generally each
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| D | crc32.txt | 3 A CRC is a long-division remainder. You add the CRC to the message,
4 and the whole thing (message+CRC) is a multiple of the given
8 is used by a lot of hardware implementations, and is why so many
14 subtract, we just xor. Thus, we tend to get a bit sloppy about
18 To produce a 32-bit CRC, the divisor is actually a 33-bit CRC polynomial.
23 Note that a CRC is computed over a string of *bits*, so you have
28 is sent last. And when appending a CRC word to a message, you should
31 Just like with ordinary division, you proceed one digit (bit) at a time.
36 and to make the XOR cancel, it's just a copy of bit 32 of the remainder.
38 When computing a CRC, we don't care about the quotient, so we can
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| D | sysfs-rules.txt | 5 by the kernel developers that the Linux kernel does not provide a stable
10 low-level userspace applications, with a new kernel release, the users
26 current kernel development. The goal of providing a stable interface
31 Parsing /proc/mounts is a waste of time. Other mount points are a
33 possibly support a SYSFS_PATH environment variable to overwrite the
40 just simply a "device". Class-, bus-, physical, ... types are just
44 The properties of a device are:
50 /sys, and always starting with with a slash
51 - all elements of a devpath must be real directories. Symlinks
56 - using or exposing symlink values as elements in a devpath string
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| D | CodingStyle | 4 This is a short document describing the preferred coding style for the
10 First off, I'd suggest printing out a copy of the GNU coding standards,
11 and NOT read it. Burn them, it's a great symbolic gesture.
24 a block of control starts and ends. Especially when you've been looking
25 at your screen for 20 straight hours, you'll find it a lot easier to see
29 the code move too far to the right, and makes it hard to read on a
38 The preferred way to ease multiple indentation levels in a switch statement is
60 Don't put multiple statements on a single line unless you have
66 Don't put multiple assignments on a single line either. Kernel coding style
72 Get a decent editor and don't leave whitespace at the end of lines.
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| /Documentation/filesystems/ |
| D | mandatory-locking.txt | 11 The Linux implementation is prey to a number of difficult-to-fix race
14 - The write system call checks for a mandatory lock only once
15 at its start. It is therefore possible for a lock request to
17 A process may then see file data change even while a mandatory
19 - Similarly, an exclusive lock may be granted on a file after
20 the kernel has decided to proceed with a read, but before the
22 the file data in a state which should not have been visible
33 (and the lockf() library routine which is a wrapper around fcntl().) It is
34 normally a process' responsibility to check for locks on a file it wishes to
37 troublesome) is access to a user's mailbox. The mail user agent and the mail
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| D | sharedsubtree.txt | 33 a. shared mount
39 2a) A shared mount can be replicated to as many mountpoints and all the
44 Let's say /mnt has a mount that is shared.
56 a b c
59 a b c
61 Now let's say we mount a device at /tmp/a
62 # mount /dev/sd0 /tmp/a
64 #ls /tmp/a
67 #ls /mnt/a
72 And the same is true even when /dev/sd0 is mounted on /mnt/a. The
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| D | gfs2.txt | 6 GFS is a cluster file system. It allows a cluster of computers to
7 simultaneously use a block device that is shared between them (with FC,
8 iSCSI, NBD, etc). GFS reads and writes to the block device like a local
9 file system, but also uses a lock module to allow the computers coordinate
17 lock_nolock -- allows gfs to be used as a local file system
19 lock_dlm -- uses a distributed lock manager (dlm) for inter-node locking
25 To use gfs as a local file system, no external clustering systems are
33 and write a cluster.conf as per the documentation. For F17 and above
40 fsck.gfs2 to repair a filesystem
41 gfs2_grow to expand a filesystem online
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| /Documentation/vm/ |
| D | frontswap.txt | 1 Frontswap provides a "transcendent memory" interface for swap pages.
3 swapped pages are saved in RAM (or a RAM-like device) instead of a swap disk.
8 See the LWN.net article "Transcendent memory in a nutshell" for a detailed
13 a "backing" store for a swap device. The storage is assumed to be
14 a synchronous concurrency-safe page-oriented "pseudo-RAM device" conforming
33 Once a page is successfully stored, a matching load on the page will normally
34 succeed. So when the kernel finds itself in a situation where it needs
35 to swap out a page, it first attempts to use frontswap. If the store returns
37 a disk write and, if the data is later read back, a disk read are avoided.
38 If a store returns failure, transcendent memory has rejected the data, and the
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| D | cleancache.txt | 3 Cleancache is a new optional feature provided by the VFS layer that
5 many workloads in many environments at a negligible cost.
7 Cleancache can be thought of as a page-granularity victim cache for clean
10 PFRA "evicts" a page, it first attempts to use cleancache code to
15 Later, when a cleancache-enabled filesystem wishes to access a page
16 in a file on disk, it first checks cleancache to see if it already
18 and a disk access is avoided.
30 passing a pointer to a cleancache_ops structure with funcs set appropriately.
42 Mounting a cleancache-enabled filesystem should call "init_fs" to obtain a
44 a negative return value indicates failure. A "put_page" will copy a
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| /Documentation/cgroups/ |
| D | cgroups.txt | 41 Control Groups provide a mechanism for aggregating/partitioning sets of
47 A *cgroup* associates a set of tasks with a set of parameters for one
50 A *subsystem* is a module that makes use of the task grouping
52 particular ways. A subsystem is typically a "resource controller" that
53 schedules a resource or applies per-cgroup limits, but it may be
54 anything that wants to act on a group of processes, e.g. a
57 A *hierarchy* is a set of cgroups arranged in a tree, such that
59 hierarchy, and a set of subsystems; each subsystem has system-specific
64 cgroups. Each hierarchy is a partition of all tasks in the system.
68 which cgroup a task is assigned, and list the task PIDs assigned to
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| /Documentation/i2c/ |
| D | smbus-protocol | 4 The following is a summary of the SMBus protocol. It applies to
10 which is a subset from the I2C protocol. Fortunately, many devices use
13 If you write a driver for some I2C device, please try to use the SMBus
20 Below is a list of SMBus protocol operations, and the functions executing
22 don't match these function names. For some of the operations which pass a
24 a different protocol operation entirely.
26 Each transaction type corresponds to a functionality flag. Before calling a
27 transaction function, a device driver should always check (just once) for
41 get a 10 bit I2C address.
42 Comm (8 bits): Command byte, a data byte which often selects a register on
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| /Documentation/networking/ |
| D | rxrpc.txt | 5 The RxRPC protocol driver provides a reliable two-phase transport on top of UDP
35 RxRPC is a two-layer protocol. There is a session layer which provides
37 layer, but implements a real network protocol; and there's the presentation
55 making the session part of it a Linux network protocol (AF_RXRPC).
57 (2) A two-phase protocol. The client transmits a blob (the request) and then
58 receives a blob (the reply), and the server receives the request and then
78 (2) provided with a protocol of the type of underlying transport they're going
100 (*) Each connection goes to a particular "service". A connection may not go
102 a port number. AF_RXRPC permits multiple services to share an endpoint.
104 (*) Client-originating packets are marked, thus a transport endpoint can be
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| D | scaling.txt | 7 This document describes a set of complementary techniques in the Linux
24 (multi-queue). On reception, a NIC can send different packets to different
26 applying a filter to each packet that assigns it to one of a small number
27 of logical flows. Packets for each flow are steered to a separate receive
34 The filter used in RSS is typically a hash function over the network
35 and/or transport layer headers-- for example, a 4-tuple hash over
36 IP addresses and TCP ports of a packet. The most common hardware
37 implementation of RSS uses a 128-entry indirection table where each entry
38 stores a queue number. The receive queue for a packet is determined
40 packet (usually a Toeplitz hash), taking this number as a key into the
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| /Documentation/usb/ |
| D | WUSB-Design-overview.txt | 16 You should have received a copy of the GNU General Public License
27 This code implements a Ultra Wide Band stack for Linux, as well as
35 2. DWA: Device Wired Adaptor, a Wireless USB hub for wired
56 UWB is a wide-band communication protocol that is to serve also as the
61 UWB uses a band from roughly 3 to 10 GHz, transmitting at a max of
64 a bunch of ~1.5 GHz wide channels (or band groups) composed of three
67 driver considers them all a single one.
72 each superframe there is a Beacon Period (BP), where every device
73 transmit its beacon on a single MAS. The length of the BP depends on how
76 Devices have a MAC (fixed, 48 bit address) and a device (changeable, 16
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| /Documentation/development-process/ |
| D | 5.Posting | 5 kernel. Unsurprisingly, the kernel development community has evolved a set
16 There is a constant temptation to avoid posting patches before they are
17 completely "ready." For simple patches, that is not a problem. If the
18 work being done is complex, though, there is a lot to be gained by getting
20 consider posting in-progress work, or even making a git tree available so
23 When posting code which is not yet considered ready for inclusion, it is a
32 There are a number of things which should be done before you consider
44 benchmarks showing what the impact (or benefit) of your change is; a
48 for an employer, the employer likely has a right to the work and must be
51 As a general rule, putting in some extra thought before posting code almost
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| /Documentation/accounting/ |
| D | delay-accounting.txt | 5 for some kernel resource to become available e.g. a
6 runnable task may wait for a free CPU to run on.
9 the delays experienced by a task while
11 a) waiting for a CPU (while being runnable)
19 Such delays provide feedback for setting a task's cpu priority,
21 important tasks could be a trigger for raising its corresponding priority.
24 delay statistics aggregated for all tasks (or threads) belonging to a
25 thread group (corresponding to a traditional Unix process). This is a commonly
30 statistics of a task are available both during its lifetime as well as on its
38 in detail in a separate document in this directory. Taskstats returns a
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| /Documentation/devicetree/ |
| D | booting-without-of.txt | 31 a) The root node
40 V - Recommendations for a bootloader
42 VI - System-on-a-chip devices and nodes
44 2) Representing devices without a current OF specification
63 clarifies the fact that a lot of things are
64 optional, the kernel only requires a very
73 String block now has a size, and full path
92 - Correct a few more alignment constraints
93 - Add a chapter about the device-tree
125 point and the way a new platform should be added to the kernel. The
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| /Documentation/security/ |
| D | keys.txt | 9 Keyrings are permitted; these are a special type of key that can hold links to
10 other keys. Processes each have three standard keyring subscriptions that a
27 - Defining a key type
39 Each key has a number of attributes:
43 - A description (for matching a key in a search).
50 (*) Each key is issued a serial number of type key_serial_t that is unique for
54 Userspace programs can use a key's serial numbers as a way to gain access
57 (*) Each key is of a defined "type". Types must be registered inside the
58 kernel by a kernel service (such as a filesystem) before keys of that type
61 Key types are represented in the kernel by struct key_type. This defines a
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| D | Smack.txt | 7 Smack is a kernel based implementation of mandatory access
21 The kernel component of Smack is implemented as a Linux
25 It is safe to run a Smack kernel under a "vanilla" distribution.
63 the label given to a new filesystem object will be the label
66 The Smack label of a process that execs a program file with
69 Don't allow the file to be mmapped by a process whose Smack
70 label does not allow all of the access permitted to a process
71 with the label contained in this attribute. This is a very
75 on a directory when an object is created in the directory and
79 creating process. If the object being created is a directory
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| /Documentation/device-mapper/ |
| D | cache.txt | 4 dm-cache is a device mapper target written by Joe Thornber, Heinz
7 It aims to improve performance of a block device (eg, a spindle) by
8 dynamically migrating some of its data to a faster, smaller device
13 a thin-provisioning pool. Caching solutions that are integrated more
19 The decision as to what data to migrate and when is left to a plug-in
22 scenarios (eg. a vm image server).
27 Migration - Movement of the primary copy of a logical block from one
32 The origin device always contains a copy of the logical block, which
53 e.g. as a mirror for extra robustness.
58 The origin is divided up into blocks of a fixed size. This block size
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| /Documentation/rapidio/ |
| D | rapidio.txt | 5 The RapidIO standard is a packet-based fabric interconnect standard designed for
27 A typical RapidIO network is a combination of endpoints and switches.
34 A master port (or mport) is a RapidIO interface controller that is local to the
37 by a rio_mport data structure. This structure contains master port specific
38 resources such as mailboxes and doorbells. The rio_mport also includes a unique
39 host device ID that is valid when a master port is configured as an enumerating
43 that provide functionality defined for this subsystem. To provide a hardware
57 A RapidIO switch is a special class of device that routes packets between its
58 ports towards their final destination. The packet destination port within a
70 A RapidIO network is a combination of interconnected endpoint and switch devices.
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| /Documentation/scheduler/ |
| D | sched-bwc.txt | 7 CFS bandwidth control is a CONFIG_FAIR_GROUP_SCHED extension which allows the
8 specification of the maximum CPU bandwidth available to a group or hierarchy.
10 The bandwidth allowed for a group is specified using a quota and period. Within
11 each given "period" (microseconds), a group is allowed to consume only up to
12 "quota" microseconds of CPU time. When the CPU bandwidth consumption of a
19 transferred to cpu-local "silos" on a demand basis. The amount transferred
26 cpu.cfs_quota_us: the total available run-time within a period (in microseconds)
27 cpu.cfs_period_us: the length of a period (in microseconds)
35 bandwidth restriction in place, such a group is described as an unconstrained
42 bandwidth limits are used in a hierarchical fashion, these are explained in
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