diff options
Diffstat (limited to 'Documentation/filesystems')
| -rw-r--r-- | Documentation/filesystems/autofs4.txt | 12 | ||||
| -rw-r--r-- | Documentation/filesystems/bfs.txt | 2 | ||||
| -rw-r--r-- | Documentation/filesystems/conf.py | 10 | ||||
| -rw-r--r-- | Documentation/filesystems/index.rst | 317 | ||||
| -rw-r--r-- | Documentation/filesystems/nfs/idmapper.txt | 2 | ||||
| -rw-r--r-- | Documentation/filesystems/nfs/pnfs.txt | 37 | ||||
| -rw-r--r-- | Documentation/filesystems/overlayfs.txt | 9 | ||||
| -rw-r--r-- | Documentation/filesystems/sysfs-pci.txt | 15 | ||||
| -rw-r--r-- | Documentation/filesystems/vfs.txt | 3 |
9 files changed, 356 insertions, 51 deletions
diff --git a/Documentation/filesystems/autofs4.txt b/Documentation/filesystems/autofs4.txt index f10dd590f69f..8444dc3d57e8 100644 --- a/Documentation/filesystems/autofs4.txt +++ b/Documentation/filesystems/autofs4.txt @@ -316,7 +316,7 @@ 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; + autofs_wqt_t wait_queue_entry_token; __u32 dev; __u64 ino; __u32 uid; @@ -341,12 +341,12 @@ The pipe will be set to "packet mode" (equivalent to passing `O_DIRECT`) to _pipe2(2)_ so that a read from the pipe will return at most one packet, and any unread portion of a packet will be discarded. -The `wait_queue_token` is a unique number which can identify a +The `wait_queue_entry_token` is a unique number which can identify a particular request to be acknowledged. When a message is sent over the pipe the affected dentry is marked as either "active" or "expiring" and other accesses to it block until the message is acknowledged using one of the ioctls below and the relevant -`wait_queue_token`. +`wait_queue_entry_token`. Communicating with autofs: root directory ioctls ------------------------------------------------ @@ -358,7 +358,7 @@ 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 + to the ioctl command is the "wait_queue_entry_token" number corresponding to the notification being acknowledged. - **AUTOFS_IOC_FAIL**: similar to above, but indicates failure with the error code `ENOENT`. @@ -382,14 +382,14 @@ The available ioctl commands are: struct autofs_packet_expire_multi { int proto_version; /* Protocol version */ int type; /* Type of packet */ - autofs_wqt_t wait_queue_token; + autofs_wqt_t wait_queue_entry_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` + `errno` is set to `EAGAIN`. Even though a `wait_queue_entry_token` is present in the structure, no "wait queue" is established and no acknowledgment is needed. - **AUTOFS_IOC_EXPIRE_MULTI**: This is similar to diff --git a/Documentation/filesystems/bfs.txt b/Documentation/filesystems/bfs.txt index 78043d5a8fc3..843ce91a2e40 100644 --- a/Documentation/filesystems/bfs.txt +++ b/Documentation/filesystems/bfs.txt @@ -54,4 +54,4 @@ The first 4 bytes should be 0x1badface. If you have any patches, questions or suggestions regarding this BFS implementation please contact the author: -Tigran Aivazian <[email protected]> +Tigran Aivazian <[email protected]> diff --git a/Documentation/filesystems/conf.py b/Documentation/filesystems/conf.py new file mode 100644 index 000000000000..ea44172af5c4 --- /dev/null +++ b/Documentation/filesystems/conf.py @@ -0,0 +1,10 @@ +# -*- coding: utf-8; mode: python -*- + +project = "Linux Filesystems API" + +tags.add("subproject") + +latex_documents = [ + ('index', 'filesystems.tex', project, + 'The kernel development community', 'manual'), +] diff --git a/Documentation/filesystems/index.rst b/Documentation/filesystems/index.rst new file mode 100644 index 000000000000..256e10eedba4 --- /dev/null +++ b/Documentation/filesystems/index.rst @@ -0,0 +1,317 @@ +===================== +Linux Filesystems API +===================== + +The Linux VFS +============= + +The Filesystem types +-------------------- + +.. kernel-doc:: include/linux/fs.h + :internal: + +The Directory Cache +------------------- + +.. kernel-doc:: fs/dcache.c + :export: + +.. kernel-doc:: include/linux/dcache.h + :internal: + +Inode Handling +-------------- + +.. kernel-doc:: fs/inode.c + :export: + +.. kernel-doc:: fs/bad_inode.c + :export: + +Registration and Superblocks +---------------------------- + +.. kernel-doc:: fs/super.c + :export: + +File Locks +---------- + +.. kernel-doc:: fs/locks.c + :export: + +.. kernel-doc:: fs/locks.c + :internal: + +Other Functions +--------------- + +.. kernel-doc:: fs/mpage.c + :export: + +.. kernel-doc:: fs/namei.c + :export: + +.. kernel-doc:: fs/buffer.c + :export: + +.. kernel-doc:: block/bio.c + :export: + +.. kernel-doc:: fs/seq_file.c + :export: + +.. kernel-doc:: fs/filesystems.c + :export: + +.. kernel-doc:: fs/fs-writeback.c + :export: + +.. kernel-doc:: fs/block_dev.c + :export: + +The proc filesystem +=================== + +sysctl interface +---------------- + +.. kernel-doc:: kernel/sysctl.c + :export: + +proc filesystem interface +------------------------- + +.. kernel-doc:: fs/proc/base.c + :internal: + +Events based on file descriptors +================================ + +.. kernel-doc:: fs/eventfd.c + :export: + +The Filesystem for Exporting Kernel Objects +=========================================== + +.. kernel-doc:: fs/sysfs/file.c + :export: + +.. kernel-doc:: fs/sysfs/symlink.c + :export: + +The debugfs filesystem +====================== + +debugfs interface +----------------- + +.. kernel-doc:: fs/debugfs/inode.c + :export: + +.. kernel-doc:: fs/debugfs/file.c + :export: + +The Linux Journalling API +========================= + +Overview +-------- + +Details +~~~~~~~ + +The journalling layer is easy to use. You need to first of all create a +journal_t data structure. There are two calls to do this dependent on +how you decide to allocate the physical media on which the journal +resides. The :c:func:`jbd2_journal_init_inode` call is for journals stored in +filesystem inodes, or the :c:func:`jbd2_journal_init_dev` call can be used +for journal stored on a raw device (in a continuous range of blocks). A +journal_t is a typedef for a struct pointer, so when you are finally +finished make sure you call :c:func:`jbd2_journal_destroy` on it to free up +any used kernel memory. + +Once you have got your journal_t object you need to 'mount' or load the +journal file. The journalling layer expects the space for the journal +was already allocated and initialized properly by the userspace tools. +When loading the journal you must call :c:func:`jbd2_journal_load` to process +journal contents. If the client file system detects the journal contents +does not need to be processed (or even need not have valid contents), it +may call :c:func:`jbd2_journal_wipe` to clear the journal contents before +calling :c:func:`jbd2_journal_load`. + +Note that jbd2_journal_wipe(..,0) calls +:c:func:`jbd2_journal_skip_recovery` for you if it detects any outstanding +transactions in the journal and similarly :c:func:`jbd2_journal_load` will +call :c:func:`jbd2_journal_recover` if necessary. I would advise reading +:c:func:`ext4_load_journal` in fs/ext4/super.c for examples on this stage. + +Now you can go ahead and start modifying the underlying filesystem. +Almost. + +You still need to actually journal your filesystem changes, this is done +by wrapping them into transactions. Additionally you also need to wrap +the modification of each of the buffers with calls to the journal layer, +so it knows what the modifications you are actually making are. To do +this use :c:func:`jbd2_journal_start` which returns a transaction handle. + +:c:func:`jbd2_journal_start` and its counterpart :c:func:`jbd2_journal_stop`, +which indicates the end of a transaction are nestable calls, so you can +reenter a transaction if necessary, but remember you must call +:c:func:`jbd2_journal_stop` the same number of times as +:c:func:`jbd2_journal_start` before the transaction is completed (or more +accurately leaves the update phase). Ext4/VFS makes use of this feature to +simplify handling of inode dirtying, quota support, etc. + +Inside each transaction you need to wrap the modifications to the +individual buffers (blocks). Before you start to modify a buffer you +need to call :c:func:`jbd2_journal_get_create_access()` / +:c:func:`jbd2_journal_get_write_access()` / +:c:func:`jbd2_journal_get_undo_access()` as appropriate, this allows the +journalling layer to copy the unmodified +data if it needs to. After all the buffer may be part of a previously +uncommitted transaction. At this point you are at last ready to modify a +buffer, and once you are have done so you need to call +:c:func:`jbd2_journal_dirty_metadata`. Or if you've asked for access to a +buffer you now know is now longer required to be pushed back on the +device you can call :c:func:`jbd2_journal_forget` in much the same way as you +might have used :c:func:`bforget` in the past. + +A :c:func:`jbd2_journal_flush` may be called at any time to commit and +checkpoint all your transactions. + +Then at umount time , in your :c:func:`put_super` you can then call +:c:func:`jbd2_journal_destroy` to clean up your in-core journal object. + +Unfortunately there a couple of ways the journal layer can cause a +deadlock. The first thing to note is that each task can only have a +single outstanding transaction at any one time, remember nothing commits +until the outermost :c:func:`jbd2_journal_stop`. This means you must complete +the transaction at the end of each file/inode/address etc. operation you +perform, so that the journalling system isn't re-entered on another +journal. Since transactions can't be nested/batched across differing +journals, and another filesystem other than yours (say ext4) may be +modified in a later syscall. + +The second case to bear in mind is that :c:func:`jbd2_journal_start` can block +if there isn't enough space in the journal for your transaction (based +on the passed nblocks param) - when it blocks it merely(!) needs to wait +for transactions to complete and be committed from other tasks, so +essentially we are waiting for :c:func:`jbd2_journal_stop`. So to avoid +deadlocks you must treat :c:func:`jbd2_journal_start` / +:c:func:`jbd2_journal_stop` as if they were semaphores and include them in +your semaphore ordering rules to prevent +deadlocks. Note that :c:func:`jbd2_journal_extend` has similar blocking +behaviour to :c:func:`jbd2_journal_start` so you can deadlock here just as +easily as on :c:func:`jbd2_journal_start`. + +Try to reserve the right number of blocks the first time. ;-). This will +be the maximum number of blocks you are going to touch in this +transaction. I advise having a look at at least ext4_jbd.h to see the +basis on which ext4 uses to make these decisions. + +Another wriggle to watch out for is your on-disk block allocation +strategy. Why? Because, if you do a delete, you need to ensure you +haven't reused any of the freed blocks until the transaction freeing +these blocks commits. If you reused these blocks and crash happens, +there is no way to restore the contents of the reallocated blocks at the +end of the last fully committed transaction. One simple way of doing +this is to mark blocks as free in internal in-memory block allocation +structures only after the transaction freeing them commits. Ext4 uses +journal commit callback for this purpose. + +With journal commit callbacks you can ask the journalling layer to call +a callback function when the transaction is finally committed to disk, +so that you can do some of your own management. You ask the journalling +layer for calling the callback by simply setting +``journal->j_commit_callback`` function pointer and that function is +called after each transaction commit. You can also use +``transaction->t_private_list`` for attaching entries to a transaction +that need processing when the transaction commits. + +JBD2 also provides a way to block all transaction updates via +:c:func:`jbd2_journal_lock_updates()` / +:c:func:`jbd2_journal_unlock_updates()`. Ext4 uses this when it wants a +window with a clean and stable fs for a moment. E.g. + +:: + + + jbd2_journal_lock_updates() //stop new stuff happening.. + jbd2_journal_flush() // checkpoint everything. + ..do stuff on stable fs + jbd2_journal_unlock_updates() // carry on with filesystem use. + +The opportunities for abuse and DOS attacks with this should be obvious, +if you allow unprivileged userspace to trigger codepaths containing +these calls. + +Summary +~~~~~~~ + +Using the journal is a matter of wrapping the different context changes, +being each mount, each modification (transaction) and each changed +buffer to tell the journalling layer about them. + +Data Types +---------- + +The journalling layer uses typedefs to 'hide' the concrete definitions +of the structures used. As a client of the JBD2 layer you can just rely +on the using the pointer as a magic cookie of some sort. Obviously the +hiding is not enforced as this is 'C'. + +Structures +~~~~~~~~~~ + +.. kernel-doc:: include/linux/jbd2.h + :internal: + +Functions +--------- + +The functions here are split into two groups those that affect a journal +as a whole, and those which are used to manage transactions + +Journal Level +~~~~~~~~~~~~~ + +.. kernel-doc:: fs/jbd2/journal.c + :export: + +.. kernel-doc:: fs/jbd2/recovery.c + :internal: + +Transasction Level +~~~~~~~~~~~~~~~~~~ + +.. kernel-doc:: fs/jbd2/transaction.c + +See also +-------- + +`Journaling the Linux ext2fs Filesystem, LinuxExpo 98, Stephen +Tweedie <http://kernel.org/pub/linux/kernel/people/sct/ext3/journal-design.ps.gz>`__ + +`Ext3 Journalling FileSystem, OLS 2000, Dr. Stephen +Tweedie <http://olstrans.sourceforge.net/release/OLS2000-ext3/OLS2000-ext3.html>`__ + +splice API +========== + +splice is a method for moving blocks of data around inside the kernel, +without continually transferring them between the kernel and user space. + +.. kernel-doc:: fs/splice.c + +pipes API +========= + +Pipe interfaces are all for in-kernel (builtin image) use. They are not +exported for use by modules. + +.. kernel-doc:: include/linux/pipe_fs_i.h + :internal: + +.. kernel-doc:: fs/pipe.c diff --git a/Documentation/filesystems/nfs/idmapper.txt b/Documentation/filesystems/nfs/idmapper.txt index fe03d10bb79a..b86831acd583 100644 --- a/Documentation/filesystems/nfs/idmapper.txt +++ b/Documentation/filesystems/nfs/idmapper.txt @@ -55,7 +55,7 @@ request-key will find the first matching line and corresponding program. In this case, /some/other/program will handle all uid lookups and /usr/sbin/nfs.idmap will handle gid, user, and group lookups. -See <file:Documentation/security/keys-request-key.txt> for more information +See <file:Documentation/security/keys/request-key.rst> for more information about the request-key function. diff --git a/Documentation/filesystems/nfs/pnfs.txt b/Documentation/filesystems/nfs/pnfs.txt index 8de578a98222..80dc0bdc302a 100644 --- a/Documentation/filesystems/nfs/pnfs.txt +++ b/Documentation/filesystems/nfs/pnfs.txt @@ -64,46 +64,9 @@ table which are called by the nfs-client pnfs-core to implement the different layout types. Files-layout-driver code is in: fs/nfs/filelayout/.. directory -Objects-layout-driver code is in: fs/nfs/objlayout/.. directory Blocks-layout-driver code is in: fs/nfs/blocklayout/.. directory Flexfiles-layout-driver code is in: fs/nfs/flexfilelayout/.. directory -objects-layout setup --------------------- - -As part of the full STD implementation the objlayoutdriver.ko needs, at times, -to automatically login to yet undiscovered iscsi/osd devices. For this the -driver makes up-calles to a user-mode script called *osd_login* - -The path_name of the script to use is by default: - /sbin/osd_login. -This name can be overridden by the Kernel module parameter: - objlayoutdriver.osd_login_prog - -If Kernel does not find the osd_login_prog path it will zero it out -and will not attempt farther logins. An admin can then write new value -to the objlayoutdriver.osd_login_prog Kernel parameter to re-enable it. - -The /sbin/osd_login is part of the nfs-utils package, and should usually -be installed on distributions that support this Kernel version. - -The API to the login script is as follows: - Usage: $0 -u <URI> -o <OSDNAME> -s <SYSTEMID> - Options: - -u target uri e.g. iscsi://<ip>:<port> - (always exists) - (More protocols can be defined in the future. - The client does not interpret this string it is - passed unchanged as received from the Server) - -o osdname of the requested target OSD - (Might be empty) - (A string which denotes the OSD name, there is a - limit of 64 chars on this string) - -s systemid of the requested target OSD - (Might be empty) - (This string, if not empty is always an hex - representation of the 20 bytes osd_system_id) - blocks-layout setup ------------------- diff --git a/Documentation/filesystems/overlayfs.txt b/Documentation/filesystems/overlayfs.txt index 634d03e20c2d..c9e884b52698 100644 --- a/Documentation/filesystems/overlayfs.txt +++ b/Documentation/filesystems/overlayfs.txt @@ -21,12 +21,19 @@ from accessing the corresponding object from the original filesystem. This is most obvious from the 'st_dev' field returned by stat(2). While directories will report an st_dev from the overlay-filesystem, -all non-directory objects will report an st_dev from the lower or +non-directory objects may report an st_dev from the lower filesystem or upper filesystem that is providing the object. Similarly st_ino will only be unique when combined with st_dev, and both of these can change over the lifetime of a non-directory object. Many applications and tools ignore these values and will not be affected. +In the special case of all overlay layers on the same underlying +filesystem, all objects will report an st_dev from the overlay +filesystem and st_ino from the underlying filesystem. This will +make the overlay mount more compliant with filesystem scanners and +overlay objects will be distinguishable from the corresponding +objects in the original filesystem. + Upper and Lower --------------- diff --git a/Documentation/filesystems/sysfs-pci.txt b/Documentation/filesystems/sysfs-pci.txt index 6ea1ceda6f52..06f1d64c6f70 100644 --- a/Documentation/filesystems/sysfs-pci.txt +++ b/Documentation/filesystems/sysfs-pci.txt @@ -113,9 +113,18 @@ Supporting PCI access on new platforms -------------------------------------- In order to support PCI resource mapping as described above, Linux platform -code must define HAVE_PCI_MMAP and provide a pci_mmap_page_range function. -Platforms are free to only support subsets of the mmap functionality, but -useful return codes should be provided. +code should ideally define ARCH_GENERIC_PCI_MMAP_RESOURCE and use the generic +implementation of that functionality. To support the historical interface of +mmap() through files in /proc/bus/pci, platforms may also set HAVE_PCI_MMAP. + +Alternatively, platforms which set HAVE_PCI_MMAP may provide their own +implementation of pci_mmap_page_range() instead of defining +ARCH_GENERIC_PCI_MMAP_RESOURCE. + +Platforms which support write-combining maps of PCI resources must define +arch_can_pci_mmap_wc() which shall evaluate to non-zero at runtime when +write-combining is permitted. Platforms which support maps of I/O resources +define arch_can_pci_mmap_io() similarly. Legacy resources are protected by the HAVE_PCI_LEGACY define. Platforms wishing to support legacy functionality should define it and provide diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt index 94dd27ef4a76..f42b90687d40 100644 --- a/Documentation/filesystems/vfs.txt +++ b/Documentation/filesystems/vfs.txt @@ -694,8 +694,7 @@ struct address_space_operations { write_end: After a successful write_begin, and data copy, write_end must be called. len is the original len passed to write_begin, and copied - is the amount that was able to be copied (copied == len is always true - if write_begin was called with the AOP_FLAG_UNINTERRUPTIBLE flag). + is the amount that was able to be copied. The filesystem must take care of unlocking the page and releasing it refcount, and updating i_size. |