teaching: labs: filesystems part 2: Add lab documentation #117

valighita · 2019-04-16T18:16:00Z

Signed-off-by: Valentin Ghita [email protected]

Signed-off-by: Valenting Ghita <[email protected]>

claudiughioc · 2019-04-16T18:21:46Z

Documentation/teaching/labs/filesystems_part2.rst

+An inode uniquely identifies a file on disk and holds information about it (uid, gid, access rights, access times, pointers to data blocks, etc.).
+An important aspect is that an inode does not have information about the file name (it is retained by the associated ``dentry`` structure).
+
+The inode refers to a file on the disk. To refer an open file (associated with a file descriptor within a process), the :c:type:`struct file` structure is used.


for consistency use "struct dentry" above as you do here

claudiughioc · 2019-04-16T18:23:19Z

Documentation/teaching/labs/filesystems_part2.rst

+The inode structure
+-------------------
+
+The inode structure is the same for all file systems. In general, file systems also have particular information. These are referenced through the ``i_private`` field of the structure.


Suggest replacing "particular" with "private"

claudiughioc · 2019-04-16T18:24:54Z

Documentation/teaching/labs/filesystems_part2.rst

+
+Some of the important fields of :c:type:`struct inode` are:
+
+  * ``i_sb`` : The superblock structure of the file system to which the inode belongs to.


"the superblock structure of the file system the inode belongs to"

claudiughioc · 2019-04-16T18:27:15Z

Documentation/teaching/labs/filesystems_part2.rst

+
+  * ``i_size``: file/directory/etc. size in bytes
+  * ``i_mtime``, ``i_atime``, ``i_ctime``: change, access, and creation time
+  * ``i_nlink``: the number of names entries (dentries) that use this inode; for file systems without links (either hard or symbolic) is always set to 1


Missing the subject here, I suggest adding "this is always set to 1"

claudiughioc · 2019-04-16T18:27:33Z

Documentation/teaching/labs/filesystems_part2.rst

+  * ``i_size``: file/directory/etc. size in bytes
+  * ``i_mtime``, ``i_atime``, ``i_ctime``: change, access, and creation time
+  * ``i_nlink``: the number of names entries (dentries) that use this inode; for file systems without links (either hard or symbolic) is always set to 1
+  * ``i_blocks``: the number of blocks used by the file (all blocks, not just data); is only used by the quota subsystem


This is only...

claudiughioc · 2019-04-16T18:30:09Z

Documentation/teaching/labs/filesystems_part2.rst

+
+    .. warning::
+
+      An inode created with :c:func:`new_inode` is not in the hash table, and unless you have serious reasons, you must enter it in the hash table;


This isn't very clear. "unless you have serios resons not to, you should add it in the hash table"

claudiughioc · 2019-04-16T18:33:27Z

Documentation/teaching/labs/filesystems_part2.rst

+One of the main inode operations is obtaining an inode (the :c:type:`struct inode` in VFS).
+Until version ``2.6.24`` of the Linux kernel, the developer defined a ``read_inode`` function.
+Starting with version ``2.6.25``, the developer must define a ``<fsname>_iget`` where ``<fsname>`` is the name of the file system.
+This function is responsible for finding the VFS inode if it exists or creating a new one and filling it with the information from the disk.


responsible with*

claudiughioc · 2019-04-16T18:34:45Z

Documentation/teaching/labs/filesystems_part2.rst

+Superoperations
+^^^^^^^^^^^^^^^
+
+Many of the superoperations (components of the :c:type:`struct super_operations` structure used by the superbloc) are used when working with inodes. These operations are described next:


superblock*

claudiughioc · 2019-04-16T18:36:36Z

Documentation/teaching/labs/filesystems_part2.rst

+  * ``evict_inode``: removes any information about the inode with the number received in the ``i_ino`` field from the disk and memory (both the inode on the disk and the associated data blocks). This involves performing the following operations:
+
+    * delete the inode from the disk;
+    * updates disk bitmaps (if any)


claudiughioc · 2019-04-16T18:37:22Z

Documentation/teaching/labs/filesystems_part2.rst

+
+    * delete the inode from the disk;
+    * updates disk bitmaps (if any)
+    * delete the inode the page cache by calling :c:func:`truncate_inode_pages`;


delete the inode from the page cache

claudiughioc · 2019-04-16T18:42:41Z

Documentation/teaching/labs/filesystems_part2.rst

+The file structure
+==================
+
+The ``file`` structure corresponds to a file open by a process and exists only in memory, being associated with an inode


Missing period after the first sentence.

claudiughioc · 2019-04-16T18:43:02Z

Documentation/teaching/labs/filesystems_part2.rst

+==================
+
+The ``file`` structure corresponds to a file open by a process and exists only in memory, being associated with an inode
+It is the VFS entity closest to user-space; the structure fields contain familiar information of a user-space file (access mode, file position, etc.) and the operations with it are known system calls (``read``, ``write`` , etc.).


It is the closest VFS entity to user-space

claudiughioc · 2019-04-16T18:48:06Z

Documentation/teaching/labs/filesystems_part2.rst

+           return generic_block_bmap(mapping, block, minix_get_block);
+  }
+
+All that needs to be done is implement :c:type:`minix_get_block`, which has to translate a block of a file into a block on the device.


is to implement

claudiughioc · 2019-04-16T18:48:39Z

Documentation/teaching/labs/filesystems_part2.rst

+All that needs to be done is implement :c:type:`minix_get_block`, which has to translate a block of a file into a block on the device.
+If the flag ``create`` received as a parameter is set, a new block must be allocated.
+In case a new block is created, the bit map must be updated accordingly.
+To notify the kernel not to read the block from the disk, ``bh`` must be marked bh with :c:func:`set_buffer_new`. The buffer must be associated with the block through :c:func:`map_bh`.


claudiughioc · 2019-04-16T18:51:20Z

Documentation/teaching/labs/filesystems_part2.rst

+  * ``d_make_root``: allocates the root dentry. It is generally used in the function that is called to read the superblock (``fill_super``), which must initialize the root directory.
+    So the root inode is obtained from the superblock and is used as an argument to this function, to fill the ``s_root`` field from the :c:type:`struct super_block` structure.
+  * ``d_add``: associates a dentry with an inode; the dentry received as a parameter in the calls discussed above signifies the entry (name, length) that needs to be created. This function will be used when creating/loading a new inode that does not have a dentry associated with it and has not yet been introduced to the hash (at ``lookup``);
+  * ``d_instantiate``: The lighter version of the previous call, in which the dentry was previously added in hash.


use the term hash table, both here and above

claudiughioc · 2019-04-16T18:52:25Z

Documentation/teaching/labs/filesystems_part2.rst

+
+.. warning::
+
+  ``d_instantiate`` must be used for create calls (``mkdir``, ``mknod``, ``rename``, ``symlink``) and  NOT ``d_add``.


must be used to implement:...

claudiughioc · 2019-04-16T18:53:24Z

Documentation/teaching/labs/filesystems_part2.rst

+In the minix case, the function is :c:func:`minix_create`.
+This function is called by the ``open`` and ``creat`` system calls. Such a function performs the following operations:
+
+  #. Introduces a new entry into the physical structure on the disk; the update of the bit maps on the disk must bot be forgotten.


Signed-off-by: Valentin Ghita <[email protected]>

teaching: labs: filesystems part 2: Add lab documentation

fa9acb6

Signed-off-by: Valenting Ghita <[email protected]>

valighita requested review from claudiughioc, dbaluta, mateiuli, razvand, Sergiu121 and tavip April 16, 2019 18:16

tavip pushed a commit to linux-kernel-labs/linux-kernel-labs.github.io that referenced this pull request Apr 16, 2019

Publish pull/117 (built from linux-kernel-labs/linux#117)

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claudiughioc reviewed Apr 16, 2019

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teaching: labs: filesystems part 2: Fixes

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Signed-off-by: Valentin Ghita <[email protected]>

tavip pushed a commit to linux-kernel-labs/linux-kernel-labs.github.io that referenced this pull request Apr 16, 2019

Publish pull/117 (built from linux-kernel-labs/linux#117)

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valighita merged commit e118554 into linux-kernel-labs:master Apr 16, 2019

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teaching: labs: filesystems part 2: Add lab documentation #117

teaching: labs: filesystems part 2: Add lab documentation #117

valighita commented Apr 16, 2019 •

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claudiughioc Apr 16, 2019

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claudiughioc Apr 16, 2019

claudiughioc Apr 16, 2019

claudiughioc Apr 16, 2019

claudiughioc Apr 16, 2019


		Some of the important fields of :c:type:`struct inode` are:

		* ``i_sb`` : The superblock structure of the file system to which the inode belongs to.


		.. warning::

		An inode created with :c:func:`new_inode` is not in the hash table, and unless you have serious reasons, you must enter it in the hash table;


		.. warning::

		``d_instantiate`` must be used for create calls (``mkdir``, ``mknod``, ``rename``, ``symlink``) and NOT ``d_add``.

teaching: labs: filesystems part 2: Add lab documentation #117

teaching: labs: filesystems part 2: Add lab documentation #117

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valighita commented Apr 16, 2019 •

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claudiughioc Apr 16, 2019 •

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