[Linux-kernel-mentees] [RFC PATCH] convert autofs.txt to reST
Jaskaran Singh
jaskaransingh7654321 at gmail.com
Wed Nov 13 07:38:46 UTC 2019
On Wed, 2019-11-13 at 12:58 +0530, Jaskaran Singh wrote:
> This patch converts autofs.txt to reST.
>
> - Most of the changes pertain to reST formatting.
> - Some of the code snippets are updated to reflect current source.
> - A definition of the autofs packet header has been added in the
> chapter
> "Communicating with autofs: the event pipe".
> - An indentation of an 8 space tab has been added wherever suitable,
> so
> as to maintain consistency.
> - Removed indentation of the description of the ioctls which are
> similar
> to the AUTOFS_IOC ioctls, as it does not come out quite right in
> HTML.
>
> Signed-off-by: Jaskaran Singh <jaskaransingh7654321 at gmail.com>
> ---
> .../filesystems/{autofs.txt => autofs.rst} | 258 ++++++++++----
> ----
> Documentation/filesystems/index.rst | 1 +
> 2 files changed, 140 insertions(+), 119 deletions(-)
> rename Documentation/filesystems/{autofs.txt => autofs.rst} (77%)
>
> diff --git a/Documentation/filesystems/autofs.txt
> b/Documentation/filesystems/autofs.rst
> similarity index 77%
> rename from Documentation/filesystems/autofs.txt
> rename to Documentation/filesystems/autofs.rst
> index 3af38c7fd26d..a130cba76f07 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
> @@ -52,7 +49,7 @@ 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
> +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.
>
> @@ -80,7 +77,7 @@ 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 +198,7 @@ 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 +298,7 @@ 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 +314,39 @@ 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 +363,7 @@ 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 +371,66 @@ 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 +440,9 @@ 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 +480,50 @@ 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 +547,7 @@ 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 +562,18 @@ 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
Forgot to add the correct subject on this, please ignore.
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