From d17bb4620f90f81d8a8a45c3d025c679a1b5efcd Mon Sep 17 00:00:00 2001 From: Amir Goldstein Date: Tue, 12 Dec 2023 08:19:30 +0200 Subject: overlayfs.rst: fix ReST formatting Fix some indentation issues and fix missing newlines in quoted text by converting quoted text to code blocks. Reported-by: Christian Brauner Suggested-by: Bagas Sanjaya Reviewed-by: Bagas Sanjaya Reviewed-by: Akira Yokosawa Signed-off-by: Amir Goldstein --- Documentation/filesystems/overlayfs.rst | 77 +++++++++++++++++---------------- 1 file changed, 39 insertions(+), 38 deletions(-) (limited to 'Documentation/filesystems') diff --git a/Documentation/filesystems/overlayfs.rst b/Documentation/filesystems/overlayfs.rst index 926396fdc5eb..1c244866041a 100644 --- a/Documentation/filesystems/overlayfs.rst +++ b/Documentation/filesystems/overlayfs.rst @@ -118,7 +118,7 @@ Where both upper and lower objects are directories, a merged directory is formed. At mount time, the two directories given as mount options "lowerdir" and -"upperdir" are combined into a merged directory: +"upperdir" are combined into a merged directory:: mount -t overlay overlay -olowerdir=/lower,upperdir=/upper,\ workdir=/work /merged @@ -172,12 +172,12 @@ directory is being read. This is unlikely to be noticed by many programs. seek offsets are assigned sequentially when the directories are read. -Thus if +Thus if: - - read part of a directory - - remember an offset, and close the directory - - re-open the directory some time later - - seek to the remembered offset + - read part of a directory + - remember an offset, and close the directory + - re-open the directory some time later + - seek to the remembered offset there may be little correlation between the old and new locations in the list of filenames, particularly if anything has changed in the @@ -290,9 +290,9 @@ Permission checking in the overlay filesystem follows these principles: 2) task creating the overlay mount MUST NOT gain additional privileges 3) non-mounting task MAY gain additional privileges through the overlay, - compared to direct access on underlying lower or upper filesystems + compared to direct access on underlying lower or upper filesystems -This is achieved by performing two permission checks on each access +This is achieved by performing two permission checks on each access: a) check if current task is allowed access based on local DAC (owner, group, mode and posix acl), as well as MAC checks @@ -311,11 +311,11 @@ to create setups where the consistency rule (1) does not hold; normally, however, the mounting task will have sufficient privileges to perform all operations. -Another way to demonstrate this model is drawing parallels between +Another way to demonstrate this model is drawing parallels between:: mount -t overlay overlay -olowerdir=/lower,upperdir=/upper,... /merged -and +and:: cp -a /lower /upper mount --bind /upper /merged @@ -328,7 +328,7 @@ Multiple lower layers --------------------- Multiple lower layers can now be given using the colon (":") as a -separator character between the directory names. For example: +separator character between the directory names. For example:: mount -t overlay overlay -olowerdir=/lower1:/lower2:/lower3 /merged @@ -340,13 +340,13 @@ rightmost one and going left. In the above example lower1 will be the top, lower2 the middle and lower3 the bottom layer. Note: directory names containing colons can be provided as lower layer by -escaping the colons with a single backslash. For example: +escaping the colons with a single backslash. For example:: mount -t overlay overlay -olowerdir=/a\:lower\:\:dir /merged Since kernel version v6.8, directory names containing colons can also be configured as lower layer using the "lowerdir+" mount options and the -fsconfig syscall from new mount api. For example: +fsconfig syscall from new mount api. For example:: fsconfig(fs_fd, FSCONFIG_SET_STRING, "lowerdir+", "/a:lower::dir", 0); @@ -405,7 +405,7 @@ A normal lower layer is not allowed to be below a data-only layer, so single colon separators are not allowed to the right of double colon ("::") separators. -For example: +For example:: mount -t overlay overlay -olowerdir=/l1:/l2:/l3::/do1::/do2 /merged @@ -419,7 +419,7 @@ to the absolute path of the "lower data" file in the "data-only" lower layer. Since kernel version v6.8, "data-only" lower layers can also be added using the "datadir+" mount options and the fsconfig syscall from new mount api. -For example: +For example:: fsconfig(fs_fd, FSCONFIG_SET_STRING, "lowerdir+", "/l1", 0); fsconfig(fs_fd, FSCONFIG_SET_STRING, "lowerdir+", "/l2", 0); @@ -429,7 +429,7 @@ For example: fs-verity support ----------------------- +----------------- During metadata copy up of a lower file, if the source file has fs-verity enabled and overlay verity support is enabled, then the @@ -547,15 +547,15 @@ filesystem. This is the list of cases that overlayfs doesn't currently handle: -a) POSIX mandates updating st_atime for reads. This is currently not -done in the case when the file resides on a lower layer. + a) POSIX mandates updating st_atime for reads. This is currently not + done in the case when the file resides on a lower layer. -b) If a file residing on a lower layer is opened for read-only and then -memory mapped with MAP_SHARED, then subsequent changes to the file are not -reflected in the memory mapping. + b) If a file residing on a lower layer is opened for read-only and then + memory mapped with MAP_SHARED, then subsequent changes to the file are not + reflected in the memory mapping. -c) If a file residing on a lower layer is being executed, then opening that -file for write or truncating the file will not be denied with ETXTBSY. + c) If a file residing on a lower layer is being executed, then opening that + file for write or truncating the file will not be denied with ETXTBSY. The following options allow overlayfs to act more like a standards compliant filesystem: @@ -647,12 +647,13 @@ 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 + 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 @@ -662,15 +663,15 @@ 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. + 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 @@ -773,9 +774,9 @@ Testsuite There's a testsuite originally developed by David Howells and currently maintained by Amir Goldstein at: - https://github.com/amir73il/unionmount-testsuite.git +https://github.com/amir73il/unionmount-testsuite.git -Run as root: +Run as root:: # cd unionmount-testsuite # ./run --ov --verify -- cgit v1.2.3