Writing file system

Because the file system may be mounted as read-only for different reasons which occur once in a time. So remounting file system will mount it in a normal state. This operation requires root privileges as expected. Another way to solve read-only file system error is rebooting the system. Rebooting the system make a fresh start where prevous error are cleared which may be related libraries, configuration, temporary changes etc. Rebooting the system generally checks the file system for errors and if it is errors they are fixed.

But in some cases, this may not work. Data produced by programs need to be stored somewhere for future reference, and there must be some sort of organisation so we can quickly retrieve the desired information.

A file system FS is responsible for this task and provides an abstraction over the storage devices where the data is physically stored. In this post, we will learn more about the concepts used by file systems, and how they fit together when writing your own. It is the job of the file system to make sense of it all. A file system will divide the disk into fixed-sized blocks. The FS uses the majority of these blocks to store user data, but some blocks are used to store metadata that is essential for the file system operation.

The following figure gives an example of how a file system structures the information on the disk:. The superblock stores most of the metadata about the file system, such as the following: block size, timestamps, how many blocks and files are in use and how many are free, etc. Bitmaps are one way of tracking which data blocks and inodes are free. An index in the bitmap set to 0 indicates a free slot, and an index set to 1 indicates an occupied slot.

The inode is the structure that stores metadata about a file. Attributes such as permissions, size, location of data blocks that form the file and more are saved in an inode. The inodes are stored in blocks that together form the inode table as the following figure shows. For each slot in the inode bitmap set to 1 , there will be a corresponding inode in the table.

The index of the slot is the same as the index in the table. And this explains the name inode being a short name for index node. As the name suggests, the data blocks are the blocks where the actual data belonging to a file is written. These blocks are also used for different purposes which we will see shortly. The inode needs to have a way of pointing to the data blocks that assemble the file. The simplest way is to have direct pointers. In this case, each pointer points to a block that has some of the file data.

The problem is that large files; where the size exceeds the number of direct pointers an inode can have; are not supported in this mode. One way of overcoming this issue is to use indirect pointers , which instead of storing user data they store pointers to blocks that hold user data. For larger files, another layer of indirection is added with double indirect pointers. And for even larger files, triple indirect pointers are put to use.

Research has shown that the majority of files are small [1] so 12 direct pointers would allow for files up to 48 KiB. Considering that each pointer takes 4 bytes, a single indirect pointer would then allow a file to be up to around 4 MiB:. This approach might not be very efficient for handling large files. For example, a file of MiB requires the allocation of blocks. The performance can be severely impacted in case the blocks were fragmented over the disk.

Some file systems use extents to help with this situation. Improve this answer. Whats the problem? The manifest file must be valid JSON syntax. See here : code. Peter O. Michael Michael 71 1 1 silver badge 1 1 bronze badge. Let's say I write a text file, can I open it in an external text editor somehow?

Marcel Marcel Any advice? Only disadvantage is that is limited to 5 MB, even after specifying the "unlimitedStorage" permission. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog.