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authorAmir Goldstein <amir73il@gmail.com>2023-12-12 08:19:30 +0200
committerAmir Goldstein <amir73il@gmail.com>2023-12-15 12:31:36 +0200
commitd17bb4620f90f81d8a8a45c3d025c679a1b5efcd (patch)
tree494085504e1d5f519a59b763878b7f06d5fd3b3a /Documentation/filesystems
parentoverlayfs.rst: use consistent feature names (diff)
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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 <brauner@kernel.org> Suggested-by: Bagas Sanjaya <bagasdotme@gmail.com> Reviewed-by: Bagas Sanjaya <bagasdotme@gmail.com> Reviewed-by: Akira Yokosawa <akiyks@gmail.com> Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Diffstat (limited to 'Documentation/filesystems')
-rw-r--r--Documentation/filesystems/overlayfs.rst77
1 files changed, 39 insertions, 38 deletions
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