diff options
Diffstat (limited to 'Documentation/filesystems')
| -rw-r--r-- | Documentation/filesystems/afs.txt | 17 | ||||
| -rw-r--r-- | Documentation/filesystems/dax.txt | 1 | ||||
| -rw-r--r-- | Documentation/filesystems/ext2.txt | 2 | ||||
| -rw-r--r-- | Documentation/filesystems/ext4.txt | 9 | ||||
| -rw-r--r-- | Documentation/filesystems/fscrypt.rst | 10 | ||||
| -rw-r--r-- | Documentation/filesystems/nfs/Exporting | 27 | ||||
| -rw-r--r-- | Documentation/filesystems/overlayfs.txt | 106 | ||||
| -rw-r--r-- | Documentation/filesystems/sysfs.txt | 4 | ||||
| -rw-r--r-- | Documentation/filesystems/vfat.txt | 2 |
9 files changed, 154 insertions, 24 deletions
diff --git a/Documentation/filesystems/afs.txt b/Documentation/filesystems/afs.txt index ba99b5ac4fd8..c5254f6d234d 100644 --- a/Documentation/filesystems/afs.txt +++ b/Documentation/filesystems/afs.txt @@ -7,6 +7,7 @@ Contents: - Overview. - Usage. - Mountpoints. + - Dynamic root. - Proc filesystem. - The cell database. - Security. @@ -127,6 +128,22 @@ mounted on /afs in one go by doing: umount /afs +============ +DYNAMIC ROOT +============ + +A mount option is available to create a serverless mount that is only usable +for dynamic lookup. Creating such a mount can be done by, for example: + + mount -t afs none /afs -o dyn + +This creates a mount that just has an empty directory at the root. Attempting +to look up a name in this directory will cause a mountpoint to be created that +looks up a cell of the same name, for example: + + ls /afs/grand.central.org/ + + =============== PROC FILESYSTEM =============== diff --git a/Documentation/filesystems/dax.txt b/Documentation/filesystems/dax.txt index 3be3b266be41..70cb68bed2e8 100644 --- a/Documentation/filesystems/dax.txt +++ b/Documentation/filesystems/dax.txt @@ -46,7 +46,6 @@ stall the CPU for an extended period, you should also not attempt to implement direct_access. These block devices may be used for inspiration: -- axonram: Axon DDR2 device driver - brd: RAM backed block device driver - dcssblk: s390 dcss block device driver - pmem: NVDIMM persistent memory driver diff --git a/Documentation/filesystems/ext2.txt b/Documentation/filesystems/ext2.txt index 55755395d3dc..81c0becab225 100644 --- a/Documentation/filesystems/ext2.txt +++ b/Documentation/filesystems/ext2.txt @@ -49,12 +49,10 @@ sb=n Use alternate superblock at this location. user_xattr Enable "user." POSIX Extended Attributes (requires CONFIG_EXT2_FS_XATTR). - See also http://acl.bestbits.at nouser_xattr Don't support "user." extended attributes. acl Enable POSIX Access Control Lists support (requires CONFIG_EXT2_FS_POSIX_ACL). - See also http://acl.bestbits.at noacl Don't support POSIX ACLs. nobh Do not attach buffer_heads to file pagecache. diff --git a/Documentation/filesystems/ext4.txt b/Documentation/filesystems/ext4.txt index 75236c0c2ac2..7f628b9f7c4b 100644 --- a/Documentation/filesystems/ext4.txt +++ b/Documentation/filesystems/ext4.txt @@ -202,15 +202,14 @@ inode_readahead_blks=n This tuning parameter controls the maximum the buffer cache. The default value is 32 blocks. nouser_xattr Disables Extended User Attributes. See the - attr(5) manual page and http://acl.bestbits.at/ - for more information about extended attributes. + attr(5) manual page for more information about + extended attributes. noacl This option disables POSIX Access Control List support. If ACL support is enabled in the kernel configuration (CONFIG_EXT4_FS_POSIX_ACL), ACL is enabled by default on mount. See the acl(5) manual - page and http://acl.bestbits.at/ for more information - about acl. + page for more information about acl. bsddf (*) Make 'df' act like BSD. minixdf Make 'df' act like Minix. @@ -233,7 +232,7 @@ data_err=ignore(*) Just print an error message if an error occurs data_err=abort Abort the journal if an error occurs in a file data buffer in ordered mode. -grpid Give objects the same group ID as their creator. +grpid New objects have the group ID of their parent. bsdgroups nogrpid (*) New objects have the group ID of their creator. diff --git a/Documentation/filesystems/fscrypt.rst b/Documentation/filesystems/fscrypt.rst index 776ddc655f79..cfbc18f0d9c9 100644 --- a/Documentation/filesystems/fscrypt.rst +++ b/Documentation/filesystems/fscrypt.rst @@ -448,8 +448,14 @@ astute users may notice some differences in behavior: - The st_size of an encrypted symlink will not necessarily give the length of the symlink target as required by POSIX. It will actually - give the length of the ciphertext, which may be slightly longer than - the plaintext due to the NUL-padding. + give the length of the ciphertext, which will be slightly longer + than the plaintext due to NUL-padding and an extra 2-byte overhead. + +- The maximum length of an encrypted symlink is 2 bytes shorter than + the maximum length of an unencrypted symlink. For example, on an + EXT4 filesystem with a 4K block size, unencrypted symlinks can be up + to 4095 bytes long, while encrypted symlinks can only be up to 4093 + bytes long (both lengths excluding the terminating null). Note that mmap *is* supported. This is possible because the pagecache for an encrypted file contains the plaintext, not the ciphertext. diff --git a/Documentation/filesystems/nfs/Exporting b/Documentation/filesystems/nfs/Exporting index 520a4becb75c..63889149f532 100644 --- a/Documentation/filesystems/nfs/Exporting +++ b/Documentation/filesystems/nfs/Exporting @@ -56,13 +56,25 @@ a/ A dentry flag DCACHE_DISCONNECTED which is set on any dentry that might not be part of the proper prefix. This is set when anonymous dentries are created, and cleared when a dentry is noticed to be a child of a dentry which is in the proper - prefix. - -b/ A per-superblock list "s_anon" of dentries which are the roots of - subtrees that are not in the proper prefix. These dentries, as - well as the proper prefix, need to be released at unmount time. As - these dentries will not be hashed, they are linked together on the - d_hash list_head. + prefix. If the refcount on a dentry with this flag set + becomes zero, the dentry is immediately discarded, rather than being + kept in the dcache. If a dentry that is not already in the dcache + is repeatedly accessed by filehandle (as NFSD might do), an new dentry + will be a allocated for each access, and discarded at the end of + the access. + + Note that such a dentry can acquire children, name, ancestors, etc. + without losing DCACHE_DISCONNECTED - that flag is only cleared when + subtree is successfully reconnected to root. Until then dentries + in such subtree are retained only as long as there are references; + refcount reaching zero means immediate eviction, same as for unhashed + dentries. That guarantees that we won't need to hunt them down upon + umount. + +b/ A primitive for creation of secondary roots - d_obtain_root(inode). + Those do _not_ bear DCACHE_DISCONNECTED. They are placed on the + per-superblock list (->s_roots), so they can be located at umount + time for eviction purposes. c/ Helper routines to allocate anonymous dentries, and to help attach loose directory dentries at lookup time. They are: @@ -77,7 +89,6 @@ c/ Helper routines to allocate anonymous dentries, and to help attach (such as an anonymous one created by d_obtain_alias), if appropriate. It returns NULL when the passed-in dentry is used, following the calling convention of ->lookup. - Filesystem Issues ----------------- diff --git a/Documentation/filesystems/overlayfs.txt b/Documentation/filesystems/overlayfs.txt index e6a5f4912b6d..6ea1e64d1464 100644 --- a/Documentation/filesystems/overlayfs.txt +++ b/Documentation/filesystems/overlayfs.txt @@ -190,6 +190,20 @@ Mount options: Redirects are not created and not followed (equivalent to "redirect_dir=off" if "redirect_always_follow" feature is not enabled). +When the NFS export feature is enabled, every copied up directory is +indexed by the file handle of the lower inode and a file handle of the +upper directory is stored in a "trusted.overlay.upper" extended attribute +on the index entry. On lookup of a merged directory, if the upper +directory does not match the file handle stores in the index, that is an +indication that multiple upper directories may be redirected to the same +lower directory. In that case, lookup returns an error and warns about +a possible inconsistency. + +Because lower layer redirects cannot be verified with the index, enabling +NFS export support on an overlay filesystem with no upper layer requires +turning off redirect follow (e.g. "redirect_dir=nofollow"). + + Non-directories --------------- @@ -281,9 +295,9 @@ filesystem, so both st_dev and st_ino of the file may change. Any open files referring to this inode will access the old data. -If a file with multiple hard links is copied up, then this will -"break" the link. Changes will not be propagated to other names -referring to the same inode. +Unless "inode index" feature is enabled, if a file with multiple hard +links is copied up, then this will "break" the link. Changes will not be +propagated to other names referring to the same inode. Unless "redirect_dir" feature is enabled, rename(2) on a lower or merged directory will fail with EXDEV. @@ -299,6 +313,92 @@ filesystem are not allowed. If the underlying filesystem is changed, the behavior of the overlay is undefined, though it will not result in a crash or deadlock. +When the overlay NFS export feature is enabled, overlay filesystems +behavior on offline changes of the underlying lower layer is different +than the behavior when NFS export is disabled. + +On every copy_up, an NFS file handle of the lower inode, along with the +UUID of the lower filesystem, are encoded and stored in an extended +attribute "trusted.overlay.origin" on the upper inode. + +When the NFS export feature is enabled, a lookup of a merged directory, +that found a lower directory at the lookup path or at the path pointed +to by the "trusted.overlay.redirect" extended attribute, will verify +that the found lower directory file handle and lower filesystem UUID +match the origin file handle that was stored at copy_up time. If a +found lower directory does not match the stored origin, that directory +will not be merged with the upper directory. + + + +NFS export +---------- + +When the underlying filesystems supports NFS export and the "nfs_export" +feature is enabled, an overlay filesystem may be exported to NFS. + +With the "nfs_export" feature, on copy_up of any lower object, an index +entry is created under the index directory. The index entry name is the +hexadecimal representation of the copy up origin file handle. For a +non-directory object, the index entry is a hard link to the upper inode. +For a directory object, the index entry has an extended attribute +"trusted.overlay.upper" with an encoded file handle of the upper +directory inode. + +When encoding a file handle from an overlay filesystem object, the +following rules apply: + +1. For a non-upper object, encode a lower file handle from lower inode +2. For an indexed object, encode a lower file handle from copy_up origin +3. For a pure-upper object and for an existing non-indexed upper object, + encode an upper file handle from upper inode + +The encoded overlay file handle includes: + - Header including path type information (e.g. lower/upper) + - UUID of the underlying filesystem + - Underlying filesystem encoding of underlying inode + +This encoding format is identical to the encoding format file handles that +are stored in extended attribute "trusted.overlay.origin". + +When decoding an overlay file handle, the following steps are followed: + +1. Find underlying layer by UUID and path type information. +2. Decode the underlying filesystem file handle to underlying dentry. +3. For a lower file handle, lookup the handle in index directory by name. +4. If a whiteout is found in index, return ESTALE. This represents an + overlay object that was deleted after its file handle was encoded. +5. For a non-directory, instantiate a disconnected overlay dentry from the + decoded underlying dentry, the path type and index inode, if found. +6. For a directory, use the connected underlying decoded dentry, path type + and index, to lookup a connected overlay dentry. + +Decoding a non-directory file handle may return a disconnected dentry. +copy_up of that disconnected dentry will create an upper index entry with +no upper alias. + +When overlay filesystem has multiple lower layers, a middle layer +directory may have a "redirect" to lower directory. Because middle layer +"redirects" are not indexed, a lower file handle that was encoded from the +"redirect" origin directory, cannot be used to find the middle or upper +layer directory. Similarly, a lower file handle that was encoded from a +descendant of the "redirect" origin directory, cannot be used to +reconstruct a connected overlay path. To mitigate the cases of +directories that cannot be decoded from a lower file handle, these +directories are copied up on encode and encoded as an upper file handle. +On an overlay filesystem with no upper layer this mitigation cannot be +used NFS export in this setup requires turning off redirect follow (e.g. +"redirect_dir=nofollow"). + +The overlay filesystem does not support non-directory connectable file +handles, so exporting with the 'subtree_check' exportfs configuration will +cause failures to lookup files over NFS. + +When the NFS export feature is enabled, all directory index entries are +verified on mount time to check that upper file handles are not stale. +This verification may cause significant overhead in some cases. + + Testsuite --------- diff --git a/Documentation/filesystems/sysfs.txt b/Documentation/filesystems/sysfs.txt index 9a3658cc399e..a1426cabcef1 100644 --- a/Documentation/filesystems/sysfs.txt +++ b/Documentation/filesystems/sysfs.txt @@ -154,8 +154,8 @@ static ssize_t dev_attr_show(struct kobject *kobj, struct attribute *attr, if (dev_attr->show) ret = dev_attr->show(dev, dev_attr, buf); if (ret >= (ssize_t)PAGE_SIZE) { - print_symbol("dev_attr_show: %s returned bad count\n", - (unsigned long)dev_attr->show); + printk("dev_attr_show: %pS returned bad count\n", + dev_attr->show); } return ret; } diff --git a/Documentation/filesystems/vfat.txt b/Documentation/filesystems/vfat.txt index cf51360e3a9f..91031298beb1 100644 --- a/Documentation/filesystems/vfat.txt +++ b/Documentation/filesystems/vfat.txt @@ -344,4 +344,4 @@ the following: characters in the final slot are set to Unicode 0xFFFF. Finally, note that the extended name is stored in Unicode. Each Unicode -character takes two bytes. +character takes either two or four bytes, UTF-16LE encoded. |