diff options
| author | Linus Torvalds <torvalds@linux-foundation.org> | 2019-12-02 11:51:02 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2019-12-02 11:51:02 -0800 |
| commit | 937d6eefc716a9071f0e3bada19200de1bb9d048 (patch) | |
| tree | 7b2b8e94d157ddbacc2b0712fd5d20a8b4d79c27 /Documentation/filesystems | |
| parent | 2c97b5ae83dca56718774e7b4bf9640f05d11867 (diff) | |
| parent | 36bb9778fd11173f2dd1484e4f6797365e18c1d8 (diff) | |
Merge tag 'docs-5.5a' of git://git.lwn.net/linux
Pull Documentation updates from Jonathan Corbet:
"Here are the main documentation changes for 5.5:
- Various kerneldoc script enhancements.
- More RST conversions; those are slowing down as we run out of
things to convert, but we're a ways from done still.
- Dan's "maintainer profile entry" work landed at last. Now we just
need to get maintainers to fill in the profiles...
- A reworking of the parallel build setup to work better with a
variety of systems (and to not take over huge systems entirely in
particular).
- The MAINTAINERS file is now converted to RST during the build.
Hopefully nobody ever tries to print this thing, or they will need
to load a lot of paper.
- A script and documentation making it easy for maintainers to add
Link: tags at commit time.
Also included is the removal of a bunch of spurious CR characters"
* tag 'docs-5.5a' of git://git.lwn.net/linux: (91 commits)
docs: remove a bunch of stray CRs
docs: fix up the maintainer profile document
libnvdimm, MAINTAINERS: Maintainer Entry Profile
Maintainer Handbook: Maintainer Entry Profile
MAINTAINERS: Reclaim the P: tag for Maintainer Entry Profile
docs, parallelism: Rearrange how jobserver reservations are made
docs, parallelism: Do not leak blocking mode to other readers
docs, parallelism: Fix failure path and add comment
Documentation: Remove bootmem_debug from kernel-parameters.txt
Documentation: security: core.rst: fix warnings
Documentation/process/howto/kokr: Update for 4.x -> 5.x versioning
Documentation/translation: Use Korean for Korean translation title
docs/memory-barriers.txt: Remove remaining references to mmiowb()
docs/memory-barriers.txt/kokr: Update I/O section to be clearer about CPU vs thread
docs/memory-barriers.txt/kokr: Fix style, spacing and grammar in I/O section
Documentation/kokr: Kill all references to mmiowb()
docs/memory-barriers.txt/kokr: Rewrite "KERNEL I/O BARRIER EFFECTS" section
docs: Add initial documentation for devfreq
Documentation: Document how to get links with git am
docs: Add request_irq() documentation
...
Diffstat (limited to 'Documentation/filesystems')
| -rw-r--r-- | Documentation/filesystems/autofs.rst (renamed from Documentation/filesystems/autofs.txt) | 263 | ||||
| -rw-r--r-- | Documentation/filesystems/index.rst | 1 | ||||
| -rw-r--r-- | Documentation/filesystems/locking.rst | 2 |
3 files changed, 144 insertions, 122 deletions
diff --git a/Documentation/filesystems/autofs.txt b/Documentation/filesystems/autofs.rst index 3af38c7fd26d..681c6a492bc0 100644 --- a/Documentation/filesystems/autofs.txt +++ b/Documentation/filesystems/autofs.rst @@ -1,12 +1,9 @@ -<head> -<style> p { max-width:50em} ol, ul {max-width: 40em}</style> -</head> - +===================== autofs - how it works ===================== Purpose -------- +======= The goal of autofs is to provide on-demand mounting and race free automatic unmounting of various other filesystems. This provides two @@ -28,7 +25,7 @@ key advantages: first accessed a name. Context -------- +======= The "autofs" filesystem module is only one part of an autofs system. There also needs to be a user-space program which looks up names @@ -43,7 +40,7 @@ filesystem type. Several "autofs" filesystems can be mounted and they can each be managed separately, or all managed by the same daemon. Content -------- +======= An autofs filesystem can contain 3 sorts of objects: directories, symbolic links and mount traps. Mount traps are directories with @@ -52,9 +49,10 @@ extra properties as described in the next section. Objects can only be created by the automount daemon: symlinks are created with a regular `symlink` system call, while directories and mount traps are created with `mkdir`. The determination of whether a -directory should be a mount trap or not is quite _ad hoc_, largely for -historical reasons, and is determined in part by the -*direct*/*indirect*/*offset* mount options, and the *maxproto* mount option. +directory should be a mount trap is based on a master map. This master +map is consulted by autofs to determine which directories are mount +points. Mount points can be *direct*/*indirect*/*offset*. +On most systems, the default master map is located at */etc/auto.master*. If neither the *direct* or *offset* mount options are given (so the mount is considered to be *indirect*), then the root directory is @@ -80,7 +78,7 @@ where in the tree they are (root, top level, or lower), the *maxproto*, and whether the mount was *indirect* or not. Mount Traps ---------------- +=========== A core element of the implementation of autofs is the Mount Traps which are provided by the Linux VFS. Any directory provided by a @@ -201,7 +199,7 @@ initiated or is being considered, otherwise it returns 0. Mountpoint expiry ------------------ +================= The VFS has a mechanism for automatically expiring unused mounts, much as it can expire any unused dentry information from the dcache. @@ -301,7 +299,7 @@ completed (together with removing any directories that might have been necessary), or has been aborted. Communicating with autofs: detecting the daemon ------------------------------------------------ +=============================================== There are several forms of communication between the automount daemon and the filesystem. As we have already seen, the daemon can create and @@ -317,33 +315,39 @@ If the daemon ever has to be stopped and restarted a new pgid can be provided through an ioctl as will be described below. Communicating with autofs: the event pipe ------------------------------------------ +========================================= When an autofs filesystem is mounted, the 'write' end of a pipe must be passed using the 'fd=' mount option. autofs will write notification messages to this pipe for the daemon to respond to. -For version 5, the format of the message is: - - struct autofs_v5_packet { - int proto_version; /* Protocol version */ - int type; /* Type of packet */ - autofs_wqt_t wait_queue_token; - __u32 dev; - __u64 ino; - __u32 uid; - __u32 gid; - __u32 pid; - __u32 tgid; - __u32 len; - char name[NAME_MAX+1]; +For version 5, the format of the message is:: + + struct autofs_v5_packet { + struct autofs_packet_hdr hdr; + autofs_wqt_t wait_queue_token; + __u32 dev; + __u64 ino; + __u32 uid; + __u32 gid; + __u32 pid; + __u32 tgid; + __u32 len; + char name[NAME_MAX+1]; }; -where the type is one of +And the format of the header is:: + + struct autofs_packet_hdr { + int proto_version; /* Protocol version */ + int type; /* Type of packet */ + }; - autofs_ptype_missing_indirect - autofs_ptype_expire_indirect - autofs_ptype_missing_direct - autofs_ptype_expire_direct +where the type is one of :: + + autofs_ptype_missing_indirect + autofs_ptype_expire_indirect + autofs_ptype_missing_direct + autofs_ptype_expire_direct so messages can indicate that a name is missing (something tried to access it but it isn't there) or that it has been selected for expiry. @@ -360,7 +364,7 @@ acknowledged using one of the ioctls below with the relevant `wait_queue_token`. Communicating with autofs: root directory ioctls ------------------------------------------------- +================================================ The root directory of an autofs filesystem will respond to a number of ioctls. The process issuing the ioctl must have the CAP_SYS_ADMIN @@ -368,58 +372,66 @@ capability, or must be the automount daemon. The available ioctl commands are: -- **AUTOFS_IOC_READY**: a notification has been handled. The argument - to the ioctl command is the "wait_queue_token" number - corresponding to the notification being acknowledged. -- **AUTOFS_IOC_FAIL**: similar to above, but indicates failure with - the error code `ENOENT`. -- **AUTOFS_IOC_CATATONIC**: Causes the autofs to enter "catatonic" - mode meaning that it stops sending notifications to the daemon. - This mode is also entered if a write to the pipe fails. -- **AUTOFS_IOC_PROTOVER**: This returns the protocol version in use. -- **AUTOFS_IOC_PROTOSUBVER**: Returns the protocol sub-version which - is really a version number for the implementation. -- **AUTOFS_IOC_SETTIMEOUT**: This passes a pointer to an unsigned - long. The value is used to set the timeout for expiry, and - the current timeout value is stored back through the pointer. -- **AUTOFS_IOC_ASKUMOUNT**: Returns, in the pointed-to `int`, 1 if - the filesystem could be unmounted. This is only a hint as - the situation could change at any instant. This call can be - used to avoid a more expensive full unmount attempt. -- **AUTOFS_IOC_EXPIRE**: as described above, this asks if there is - anything suitable to expire. A pointer to a packet: - - struct autofs_packet_expire_multi { - int proto_version; /* Protocol version */ - int type; /* Type of packet */ - autofs_wqt_t wait_queue_token; - int len; - char name[NAME_MAX+1]; - }; +- **AUTOFS_IOC_READY**: + a notification has been handled. The argument + to the ioctl command is the "wait_queue_token" number + corresponding to the notification being acknowledged. +- **AUTOFS_IOC_FAIL**: + similar to above, but indicates failure with + the error code `ENOENT`. +- **AUTOFS_IOC_CATATONIC**: + Causes the autofs to enter "catatonic" + mode meaning that it stops sending notifications to the daemon. + This mode is also entered if a write to the pipe fails. +- **AUTOFS_IOC_PROTOVER**: + This returns the protocol version in use. +- **AUTOFS_IOC_PROTOSUBVER**: + Returns the protocol sub-version which + is really a version number for the implementation. +- **AUTOFS_IOC_SETTIMEOUT**: + This passes a pointer to an unsigned + long. The value is used to set the timeout for expiry, and + the current timeout value is stored back through the pointer. +- **AUTOFS_IOC_ASKUMOUNT**: + Returns, in the pointed-to `int`, 1 if + the filesystem could be unmounted. This is only a hint as + the situation could change at any instant. This call can be + used to avoid a more expensive full unmount attempt. +- **AUTOFS_IOC_EXPIRE**: + as described above, this asks if there is + anything suitable to expire. A pointer to a packet:: + + struct autofs_packet_expire_multi { + struct autofs_packet_hdr hdr; + autofs_wqt_t wait_queue_token; + int len; + char name[NAME_MAX+1]; + }; - is required. This is filled in with the name of something - that can be unmounted or removed. If nothing can be expired, - `errno` is set to `EAGAIN`. Even though a `wait_queue_token` - is present in the structure, no "wait queue" is established - and no acknowledgment is needed. -- **AUTOFS_IOC_EXPIRE_MULTI**: This is similar to - **AUTOFS_IOC_EXPIRE** except that it causes notification to be - sent to the daemon, and it blocks until the daemon acknowledges. - The argument is an integer which can contain two different flags. + is required. This is filled in with the name of something + that can be unmounted or removed. If nothing can be expired, + `errno` is set to `EAGAIN`. Even though a `wait_queue_token` + is present in the structure, no "wait queue" is established + and no acknowledgment is needed. +- **AUTOFS_IOC_EXPIRE_MULTI**: + This is similar to + **AUTOFS_IOC_EXPIRE** except that it causes notification to be + sent to the daemon, and it blocks until the daemon acknowledges. + The argument is an integer which can contain two different flags. - **AUTOFS_EXP_IMMEDIATE** causes `last_used` time to be ignored - and objects are expired if the are not in use. + **AUTOFS_EXP_IMMEDIATE** causes `last_used` time to be ignored + and objects are expired if the are not in use. - **AUTOFS_EXP_FORCED** causes the in use status to be ignored - and objects are expired ieven if they are in use. This assumes - that the daemon has requested this because it is capable of - performing the umount. + **AUTOFS_EXP_FORCED** causes the in use status to be ignored + and objects are expired ieven if they are in use. This assumes + that the daemon has requested this because it is capable of + performing the umount. - **AUTOFS_EXP_LEAVES** will select a leaf rather than a top-level - name to expire. This is only safe when *maxproto* is 4. + **AUTOFS_EXP_LEAVES** will select a leaf rather than a top-level + name to expire. This is only safe when *maxproto* is 4. Communicating with autofs: char-device ioctls ---------------------------------------------- +============================================= It is not always possible to open the root of an autofs filesystem, particularly a *direct* mounted filesystem. If the automount daemon @@ -429,9 +441,9 @@ need there is a "miscellaneous" character device (major 10, minor 235) which can be used to communicate directly with the autofs filesystem. It requires CAP_SYS_ADMIN for access. -The `ioctl`s that can be used on this device are described in a separate +The 'ioctl's that can be used on this device are described in a separate document `autofs-mount-control.txt`, and are summarised briefly here. -Each ioctl is passed a pointer to an `autofs_dev_ioctl` structure: +Each ioctl is passed a pointer to an `autofs_dev_ioctl` structure:: struct autofs_dev_ioctl { __u32 ver_major; @@ -469,41 +481,50 @@ that the kernel module can support. Commands are: -- **AUTOFS_DEV_IOCTL_VERSION_CMD**: does nothing, except validate and - set version numbers. -- **AUTOFS_DEV_IOCTL_OPENMOUNT_CMD**: return an open file descriptor - on the root of an autofs filesystem. The filesystem is identified - by name and device number, which is stored in `openmount.devid`. - Device numbers for existing filesystems can be found in - `/proc/self/mountinfo`. -- **AUTOFS_DEV_IOCTL_CLOSEMOUNT_CMD**: same as `close(ioctlfd)`. -- **AUTOFS_DEV_IOCTL_SETPIPEFD_CMD**: if the filesystem is in - catatonic mode, this can provide the write end of a new pipe - in `setpipefd.pipefd` to re-establish communication with a daemon. - The process group of the calling process is used to identify the - daemon. -- **AUTOFS_DEV_IOCTL_REQUESTER_CMD**: `path` should be a - name within the filesystem that has been auto-mounted on. - On successful return, `requester.uid` and `requester.gid` will be - the UID and GID of the process which triggered that mount. -- **AUTOFS_DEV_IOCTL_ISMOUNTPOINT_CMD**: Check if path is a - mountpoint of a particular type - see separate documentation for - details. -- **AUTOFS_DEV_IOCTL_PROTOVER_CMD**: -- **AUTOFS_DEV_IOCTL_PROTOSUBVER_CMD**: -- **AUTOFS_DEV_IOCTL_READY_CMD**: -- **AUTOFS_DEV_IOCTL_FAIL_CMD**: -- **AUTOFS_DEV_IOCTL_CATATONIC_CMD**: -- **AUTOFS_DEV_IOCTL_TIMEOUT_CMD**: -- **AUTOFS_DEV_IOCTL_EXPIRE_CMD**: -- **AUTOFS_DEV_IOCTL_ASKUMOUNT_CMD**: These all have the same - function as the similarly named **AUTOFS_IOC** ioctls, except - that **FAIL** can be given an explicit error number in `fail.status` - instead of assuming `ENOENT`, and this **EXPIRE** command - corresponds to **AUTOFS_IOC_EXPIRE_MULTI**. +- **AUTOFS_DEV_IOCTL_VERSION_CMD**: + does nothing, except validate and + set version numbers. +- **AUTOFS_DEV_IOCTL_OPENMOUNT_CMD**: + return an open file descriptor + on the root of an autofs filesystem. The filesystem is identified + by name and device number, which is stored in `openmount.devid`. + Device numbers for existing filesystems can be found in + `/proc/self/mountinfo`. +- **AUTOFS_DEV_IOCTL_CLOSEMOUNT_CMD**: + same as `close(ioctlfd)`. +- **AUTOFS_DEV_IOCTL_SETPIPEFD_CMD**: + if the filesystem is in + catatonic mode, this can provide the write end of a new pipe + in `setpipefd.pipefd` to re-establish communication with a daemon. + The process group of the calling process is used to identify the + daemon. +- **AUTOFS_DEV_IOCTL_REQUESTER_CMD**: + `path` should be a + name within the filesystem that has been auto-mounted on. + On successful return, `requester.uid` and `requester.gid` will be + the UID and GID of the process which triggered that mount. +- **AUTOFS_DEV_IOCTL_ISMOUNTPOINT_CMD**: + Check if path is a + mountpoint of a particular type - see separate documentation for + details. + +- **AUTOFS_DEV_IOCTL_PROTOVER_CMD** +- **AUTOFS_DEV_IOCTL_PROTOSUBVER_CMD** +- **AUTOFS_DEV_IOCTL_READY_CMD** +- **AUTOFS_DEV_IOCTL_FAIL_CMD** +- **AUTOFS_DEV_IOCTL_CATATONIC_CMD** +- **AUTOFS_DEV_IOCTL_TIMEOUT_CMD** +- **AUTOFS_DEV_IOCTL_EXPIRE_CMD** +- **AUTOFS_DEV_IOCTL_ASKUMOUNT_CMD** + +These all have the same +function as the similarly named **AUTOFS_IOC** ioctls, except +that **FAIL** can be given an explicit error number in `fail.status` +instead of assuming `ENOENT`, and this **EXPIRE** command +corresponds to **AUTOFS_IOC_EXPIRE_MULTI**. Catatonic mode --------------- +============== As mentioned, an autofs mount can enter "catatonic" mode. This happens if a write to the notification pipe fails, or if it is @@ -527,7 +548,7 @@ Catatonic mode can only be left via the **AUTOFS_DEV_IOCTL_OPENMOUNT_CMD** ioctl on the `/dev/autofs`. The "ignore" mount option -------------------------- +========================= The "ignore" mount option can be used to provide a generic indicator to applications that the mount entry should be ignored when displaying @@ -542,18 +563,18 @@ This is intended to be used by user space programs to exclude autofs mounts from consideration when reading the mounts list. autofs, name spaces, and shared mounts --------------------------------------- +====================================== With bind mounts and name spaces it is possible for an autofs filesystem to appear at multiple places in one or more filesystem name spaces. For this to work sensibly, the autofs filesystem should -always be mounted "shared". e.g. +always be mounted "shared". e.g. :: -> `mount --make-shared /autofs/mount/point` + mount --make-shared /autofs/mount/point The automount daemon is only able to manage a single mount location for an autofs filesystem and if mounts on that are not 'shared', other locations will not behave as expected. In particular access to those -other locations will likely result in the `ELOOP` error +other locations will likely result in the `ELOOP` error :: -> Too many levels of symbolic links + Too many levels of symbolic links diff --git a/Documentation/filesystems/index.rst b/Documentation/filesystems/index.rst index 2c3a9f761205..ad6315a48d14 100644 --- a/Documentation/filesystems/index.rst +++ b/Documentation/filesystems/index.rst @@ -46,4 +46,5 @@ Documentation for filesystem implementations. .. toctree:: :maxdepth: 2 + autofs virtiofs diff --git a/Documentation/filesystems/locking.rst b/Documentation/filesystems/locking.rst index fc3a0704553c..5057e4d9dcd1 100644 --- a/Documentation/filesystems/locking.rst +++ b/Documentation/filesystems/locking.rst @@ -105,7 +105,7 @@ getattr: no listxattr: no fiemap: no update_time: no -atomic_open: exclusive +atomic_open: shared (exclusive if O_CREAT is set in open flags) tmpfile: no ============ ============================================= |