| /Documentation/process/ |
| D | management-style.rst | 14 to do with reality. It started as a lark, but that doesn't mean that it
27 making it painfully obvious to the questioner that we don't have a clue
37 Everybody thinks managers make decisions, and that decision-making is
39 manager must be to make it. That's very deep and obvious, but it's not
47 competent to make that decision for them.
51 Namely that you are in the wrong job, and that **they** should be managing
60 It helps to realize that the key difference between a big decision and a
62 can be made small by just always making sure that if you were wrong (and
67 And people will even see that as true leadership (*cough* bullshit
71 things that can't be undone. Don't get ushered into a corner from which
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| D | 6.Followthrough.rst | 8 patches. One of the biggest mistakes that even experienced kernel
9 developers can make is to conclude that their work is now done. In truth,
13 It is a rare patch which is so good at its first posting that there is no
16 code. You, as the author of that code, will be expected to work with the
17 kernel community to ensure that your code is up to the kernel's quality
32 value and why you went to the trouble of writing it. But that value
36 to substantial rewrites - come from the understanding that Linux will
49 be working on the kernel years from now, but they understand that their
54 What all of this comes down to is that, when reviewers send you comments,
55 you need to pay attention to the technical observations that they are
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| D | stable-api-nonsense.rst | 15 Please realize that this article describes the **in kernel** interfaces, not
18 The kernel to userspace interface is the one that application programs use,
19 the syscall interface. That interface is **very** stable over time, and
20 will not break. I have old programs that were built on a pre 0.9something
21 kernel that still work just fine on the latest 2.6 kernel release.
22 That interface is the one that users and application programmers can count
30 you get that only if your driver is in the main kernel tree. You also
40 It's only the odd person who wants to write a kernel driver that needs
47 that describes kernel drivers that do not have their source code
60 Assuming that we had a stable kernel source interface for the kernel, a
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| /Documentation/vm/ |
| D | active_mm.rst | 14 Cc'd to linux-kernel, because I don't write explanations all that often,
27 difference is that an anonymous address space doesn't care about the
32 The obvious use for a "anonymous address space" is any thread that
34 this category, but even "real" threads can temporarily say that for
36 and that the scheduler might as well try to avoid wasting time on
38 sync does that.
41 tsk->mm will be NULL, for the logical reason that an anonymous process
45 "stole" for such an anonymous user. For that, we have "tsk->active_mm",
48 The rule is that for a process with a real address space (ie tsk->mm is
57 To support all that, the "struct mm_struct" now has two counters: a
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| D | memory-model.rst | 12 however, that this range contains small holes that are not accessible
20 whether it is possible to manually override that default.
34 helpers that allow the conversion from PFN to `struct page` and vice
44 In the FLATMEM memory model, there is a global `mem_map` array that
52 usable until the call to :c:func:`memblock_free_all` that hands all
56 it may free parts of the `mem_map` array that do not cover the
75 things, `pg_data_t` holds the `node_mem_map` array that maps
76 physical pages belonging to that node. The `node_start_pfn` field of
77 `pg_data_t` is the number of the first page frame belonging to that
88 node hosting that page.
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| /Documentation/filesystems/ |
| D | directory-locking.rst | 12 that "inode pointer" order in the following.
25 4) rename() that is _not_ cross-directory. Locking rules: caller locks
37 * check that source is not a directory
61 The rules above obviously guarantee that all directories that are going to be
72 That ordering can change. However, the following is true:
102 blocked on source and it means that it doesn't hold any locks.
105 has a child that is also contended. Indeed, suppose that it is held by
107 is blocked on belongs to child of that object due to (1).
109 It means that one of the operations is cross-directory rename.
111 would have a contended child and we had assumed that no object is its
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| D | path-lookup.rst | 21 exploration is needed to discover, is that it is complex. There are
22 many rules, special cases, and implementation alternatives that all
25 tool that we will make extensive use of is "divide and conquer". For
40 of elements: "slashes" that are sequences of one or more "``/``"
41 characters, and "components" that are sequences of one or more
42 non-"``/``" characters. These form two kinds of paths. Those that
51 component, but that isn't always accurate: a pathname can lack both
61 it must identify a directory that already exists, otherwise an error
67 pathname that is just slashes have a final component. If it does
74 tempting to consider that to have an empty final component. In many
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| D | xfs-delayed-logging-design.txt | 12 required for objects that are frequently logged. Some parts of inodes are more
17 The reason that this is such a concern is that XFS allows multiple separate
21 "re-logging". Conceptually, this is quite simple - all it requires is that any
23 changes in the new transaction that is written to the log.
25 That is, if we have a sequence of changes A through to F, and the object was
43 that an object being relogged does not prevent the tail of the log from ever
56 progresses, ensuring that current operation never gets blocked by itself if the
59 Hence it can be seen that the relogging operation is fundamental to the correct
63 the log over and over again. Worse is the fact that objects tend to get
67 Another feature of the XFS transaction subsystem is that most transactions are
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| /Documentation/power/ |
| D | freezing-of-tasks.rst | 17 There are three per-task flags used for that, PF_NOFREEZE, PF_FROZEN
18 and PF_FREEZER_SKIP (the last one is auxiliary). The tasks that have
28 sets this variable. After this, it executes try_to_freeze_tasks() that sends a
30 All freezable tasks must react to that by calling try_to_freeze(), which
33 it loop until PF_FROZEN is cleared for it. Then, we say that the task is
40 try_to_freeze() function (defined in include/linux/freezer.h), that checks
47 that combine interruptible sleep with checking if the task is to be frozen and
69 order to clear the PF_FROZEN flag for each frozen task. Then, the tasks that
101 IV. Why do we do that?
111 filesystem-related information that must be consistent with the state of the
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| D | s2ram.rst | 11 2) If that does not help, try reading tricks.txt and
21 always it's a driver that is buggy. Thank God for the suspend/resume
22 debugging - the thing that Chuck tried to disable. That's often the _only_
25 driver that doesn't resume and recompile and reboot).
28 machine that doesn't boot) is:
49 which means that the last trace event was just before trying to resume
50 device 0000:01:00.0. Then figure out what driver is controlling that
55 the culprit may be a device from a loadable kernel module that is not loaded
63 that "radeonfb" simply cannot resume that device - it tries to set the
70 Reason for this is that the RTC is the only reliably available piece of
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| /Documentation/RCU/ |
| D | stallwarn.txt | 5 options that can be used to fine-tune the detector's operation. Finally,
28 o Booting Linux using a console connection that is too slow to
35 o Anything that prevents RCU's grace-period kthreads from running.
45 that low-priority task is not permitted to run on any other CPU,
51 o A CPU-bound real-time task in a CONFIG_PREEMPT_RT kernel that
62 help avoid this problem. However, please note that doing this
69 Note that certain high-overhead debugging options, for example
77 slow system. Note that thermal throttling and on-demand governors
81 interrupt on a CPU that is not in dyntick-idle mode. This
91 leading the realization that the CPU had failed.
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| D | rcu_dereference.txt | 14 bugs due to games that compilers and DEC Alpha can play.
18 DEC Alpha can load a pointer, dereference that pointer, and
19 return data preceding initialization that preceded the store of
31 There are a very few exceptions, namely that you can temporarily
35 bits of that pointer. This clearly means that the pointer
48 rights to substitute zero for this sort of expression, so that
53 and "b" are integers that happen to be equal, the expression
57 o If you are using RCU to protect JITed functions, so that the
62 using the same memory that was used by an earlier JITed function.
78 As before, the reason this is buggy is that relational operators
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| D | UP.rst | 6 A common misconception is that, on UP systems, the call_rcu() primitive
8 is that since there is only one CPU, it should not be necessary to
12 This document presents three examples that demonstrate exactly how bad
18 Suppose that an RCU-based algorithm scans a linked list containing
20 this same list in softirq context. Suppose that the process-context scan
40 Suppose that an RCU-based algorithm again scans a linked list containing
41 elements A, B, and C in process contexts, but that it invokes a function
42 on each element as it is scanned. Suppose further that this function
48 underlying RCU, namely that call_rcu() defers invoking its arguments until
59 Suppose that call_rcu() is invoked while holding a lock, and that the
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| /Documentation/driver-api/driver-model/ |
| D | binding.rst | 6 driver that can control it. Bus drivers have typically handled this
15 The bus type structure contains a list of all devices that are on that bus
18 list of all drivers of that bus type. When driver_register is called
27 to find one that supports it. In order to determine that, the device
28 ID of the device must match one of the device IDs that the driver
39 chance to verify that it really does support the hardware, and that
47 class, and that is set in the driver's devclass field.
63 A symlink is created in the bus's 'devices' directory that points to
66 A symlink is created in the driver's 'devices' directory that points
70 symlink is created in that directory that points to the device's
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| /Documentation/ |
| D | DMA-attributes.txt | 5 This document describes the semantics of the DMA attributes that are
21 useful, suppose that a device does a DMA write to indicate that data is
29 DMA_ATTR_WEAK_ORDERING specifies that reads and writes to the mapping
30 may be weakly ordered, that is that reads and writes may pass each other.
33 those that do not will simply ignore the attribute and exhibit default
39 DMA_ATTR_WRITE_COMBINE specifies that writes to the mapping may be
43 those that do not will simply ignore the attribute and exhibit default
51 you are guaranteeing to the platform that you have all the correct and
63 that you won't dereference the pointer returned by dma_alloc_attr(). You
64 can treat it as a cookie that must be passed to dma_mmap_attrs() and
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| /Documentation/admin-guide/pm/ |
| D | cpuidle.rst | 33 CPU idle time management operates on CPUs as seen by the *CPU scheduler* (that
35 work in the system). In its view, CPUs are *logical* units. That is, they need
38 entity which appears to be fetching instructions that belong to one sequence
43 program) at a time, it is a CPU. In that case, if the hardware is asked to
44 enter an idle state, that applies to the processor as a whole.
51 time. The entire cores are CPUs in that case and if the hardware is asked to
52 enter an idle state, that applies to the core that asked for it in the first
54 that the core belongs to (in fact, it may apply to an entire hierarchy of larger
57 remaining core asks the processor to enter an idle state, that may trigger it
59 other cores in that unit.
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| /Documentation/block/ |
| D | inline-encryption.rst | 21 - IE hardware have a limited number of "keyslots" that can be programmed
25 that specified keyslot. When possible, we want to make multiple requests with
30 to use that encryption context when it processes the bio.
39 We add a struct bio_crypt_ctx to struct bio that can represent an
47 We introduce a keyslot manager (KSM) that handles the translation from
50 upper layers. The generic mode of operation is: each device driver that wants
52 Upper layers that want to use IE on this device can then use this KSM in
55 that the device supports IE.
60 this is achieved through the :c:type:`struct keyslot_mgmt_ll_ops` that the
65 referencing that keyslot). When a new encryption context needs a keyslot, it
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| /Documentation/media/uapi/v4l/ |
| D | colorspaces.rst | 17 biology. Just because you have three numbers that describe the 'red',
18 'green' and 'blue' components of the color of a pixel does not mean that
19 you can accurately display that color. A colorspace defines what it
20 actually *means* to have an RGB value of e.g. (255, 0, 0). That is,
24 In order to do that we first need to have a good definition of color,
25 i.e. some way to uniquely and unambiguously define a color so that
27 the human eye has color receptors that are sensitive to three different
41 possible that different SPDs will result in the same stimulation of
46 between SPDs and the perceived color and that resulted in the CIE 1931
47 standard that defines spectral weighting functions that model the
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| /Documentation/maintainer/ |
| D | rebasing-and-merging.rst | 12 those tools incorrectly, but avoiding problems is not actually all that
15 One thing to be aware of in general is that, unlike many other projects,
26 within a repository. There are two different types of operations that are
43 history; used improperly, it can obscure that history and introduce bugs.
45 There are a few rules of thumb that can help developers to avoid the worst
48 - History that has been exposed to the world beyond your private system
51 work is in need of rebasing, that is usually a sign that it is not yet
54 That said, there are always exceptions. Some trees (linux-next being
58 testing services. If you do expose a branch that may be unstable in
59 this way, be sure that prospective users know not to base work on it.
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| /Documentation/filesystems/ext4/ |
| D | allocators.rst | 6 ext4 recognizes (better than ext3, anyway) that data locality is
9 that the head actuator and disk must perform to access a data block,
17 The first tool that ext4 uses to combat fragmentation is the multi-block
20 that the space will get written soon. When the file is closed, the
24 extent. A second related trick that ext4 uses is delayed allocation.
30 is that the filesystem can make better location decisions.
32 The third trick that ext4 (and ext3) uses is that it tries to keep a
38 The fourth trick is that all the inodes in a directory are placed in the
40 here is that all the files in a directory might be related, therefore it
43 The fifth trick is that the disk volume is cut up into 128MB block
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| /Documentation/firmware-guide/acpi/ |
| D | osi.rst | 10 can evaluate that method, look to see if it supports 'XYZ'
14 that OSPM supports"
22 Linux runs on two groups of machines -- those that are tested by the OEM
23 to be compatible with Linux, and those that were never tested with Linux,
26 The larger group is the systems tested to run only Windows. Not only that,
30 Experience shows that taking untested paths through the BIOS
37 Windows to its list of _OSI strings. So it is possible that additional strings
39 But it is likely that they will all eventually be added.
52 via the linux-acpi@vger.kernel.org mailing list. When that patch
55 by the OS. Linux distributors can back-port that patch for Linux
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| /Documentation/i2c/ |
| D | fault-codes.rst | 13 faults. There may be fancier recovery schemes that are appropriate in
18 result for an operation ... it doesn't indicate that anything is wrong
19 at all, just that the outcome wasn't on the "golden path".
23 the right fault code, so that it can (in turn) behave correctly.
33 Note that the descriptions here are not exhaustive. There are other
34 codes that may be returned, and other cases where these codes should
48 atomic context, when some task is already using that I2C bus
57 host. Note that even if PECs are in use, you should not rely
64 or that the reset was attempted but failed.
85 Returned by any component that can't allocate memory when
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| /Documentation/locking/ |
| D | rt-mutex-design.rst | 11 It doesn't describe the reasons why rtmutex.c exists. For that please see
13 that happen without this code, but that is in the concept to understand
17 inheritance (PI) algorithm that is used, as well as reasons for the
18 decisions that were made to implement PI in the manner that was done.
27 to use a resource that a lower priority process has (a mutex for example),
30 is something called unbounded priority inversion. That is when the high
37 that C owns and must wait and lets C run to release the lock. But in the
71 inherited priority, and A then can continue with the resource that C had.
76 Here I explain some terminology that is used in this document to help describe
77 the design that is used to implement PI.
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| /Documentation/ia64/ |
| D | mca.rst | 5 Feel free to update it with notes about any area that is not clear.
12 asking for deadlock. Also the state of structures that are protected
27 * Slave cpus that receive the MCA interrupt call down into SAL, they
32 sends an unmaskable INIT event to the slave cpus that have not
39 (and does) modify TP. It is allowed to do that as long as it resets
45 assume that the kernel stack is in a fit state to be used. Mainly
53 the kernel stack[1]. So switching to a new kernel stack means that
55 assume that current points into the struct task, switching to a new
63 tasks. The only way to do that on ia64 is to call the unwinder,
67 running or not. That is, whether it is on a cpu or is blocked. The
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| /Documentation/admin-guide/sysctl/ |
| D | user.rst | 15 limits on the number of namespaces and other objects that have
18 The primary purpose of these limits is to stop programs that
21 intention that the defaults of these limits are set high enough that
26 verified to be below the per user limit in that user namespace.
33 This recursive counting of created objects ensures that creating a
41 The maximum number of cgroup namespaces that any user in the current
47 The maximum number of ipc namespaces that any user in the current
53 The maximum number of mount namespaces that any user in the current
59 The maximum number of network namespaces that any user in the
65 The maximum number of pid namespaces that any user in the current
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