android_kernel_oneplus_sm8250/fs/exfat

exfat-linux

This exFAT filesystem module for Linux kernel is a backport of the latest Linux mainline's exFAT drivers by Samsung.

This project can be used for everyday Linux users by simply doing make && make install. Ubuntu users can simply add a PPA and start using it, without even downloading the code. This can also be directly dropped-in to an existing Linux kernel source for building the filesystem drivers inline, which should be useful for Android kernel developers.

exfat-linux has been tested with all major LTS kernels ranging from v4.9 to v5.4 and the ones Canonical uses for Ubuntu: v4.9, v4.14, v4.19, v5.4 and v4.15, v5.3, and v5.6.

It's also been tested with x86(i386), x86_64(amd64), arm32(AArch32) and arm64(AArch64).

Linux kernels since v5.4 includes an exFAT driver, but it is an extremely outdated version from 2016. This was later revised by Samsung directly with v5.7.

People on v5.7 kernel or higher can just use the bundled exFAT drivers.

People on v5.4+ are highly recommended to use this drivers.

Support for kernel versions lower than v4.9 were dropped for easier maintenance. For people interested in exFAT support for said kernels, please use the old branch. It still works nicely and it's actively being shipped to production smartphones.

exfat-linux is planned to be maintained until Android devices with v5.7+ LTS kernel become more common.

Disclaimer

● Original authorship and copyright: Samsung

● Maintainer of exfat-linux: Park Ju Hyung(arter97)

Using exfat-linux

● Ubuntu PPA

If you're an Ubuntu user, you can simply add a PPA repository and start using the exFAT module.

Ubuntu will handle upgrades automatically as well.

1. Add the exfat-linux repository

   sudo add-apt-repository ppa:arter97/exfat-linux
   sudo apt update
   

2. Install the module

   sudo apt install exfat-dkms

This will use DKMS(Dynamic Kernel Module Support) and automatically build exFAT module for your current Ubuntu installation.

● Manually installing the module

1. Download the code

   git clone https://github.com/arter97/exfat-linux
   cd exfat-linux
   

2. Build

   make

3. Install

   sudo make install

This will install the module to your currently running kernel.

If you're running a v5.4+ kernel, it is highly recommended to reboot at this point to prevent the existing staging exFAT drivers to load.

4. And finally load

   sudo modprobe exfat

If you upgrade the kernel, you'll have to repeat this process.

If you want to update exfat-linux to the latest version, you'll have to repeat this process.

● Merging the drivers to existing Linux kernel source

If you're using git, using git subtree or git submodule is highly recommended.

1. Add this repository to fs/exfat

2. Modify fs/Kconfig

 menu "DOS/FAT/NT Filesystems"

 source "fs/fat/Kconfig"
+source "fs/exfat/Kconfig"
 source "fs/ntfs/Kconfig"
 endmenu

3. Modify fs/Makefile

 obj-$(CONFIG_FAT_FS)    += fat/
+obj-$(CONFIG_EXFAT_FS)  += exfat/
 obj-$(CONFIG_BFS_FS)    += bfs/

And you're good to go!

Benchmarks

For reference, existing exFAT implementations were tested and compared on a server running Ubuntu 16.04 with Linux kernel 4.14 under a contained virtual machine.

Linux 4.14 was used as higher LTS kernels don't work with [exfat-nofuse] at the time of testing.

The new base backported from mainline is not benchmarked yet.

● Ramdisk

fio sequential I/O

Implementation	Base	Read	Write
exfat-linux	2.2.0	7042 MB/s	2173 MB/s
[exfat-nofuse]	1.2.9	6849 MB/s	1961 MB/s
exfat-fuse	N/A	3097 MB/s	1710 MB/s
ext4	N/A	7352 MB/s	3333 MB/s

fio random I/O

Implementation	Base	Read	Write
exfat-linux	2.2.0	760 MB/s	2222 MB/s
[exfat-nofuse]	1.2.9	760 MB/s	2160 MB/s
exfat-fuse	N/A	1.7 MB/s	1.6 MB/s
ext4	N/A	747 MB/s	2816 MB/s

● NVMe device

fio sequential I/O

Implementation	Base	Read	Write
exfat-linux	2.2.0	1283 MB/s	1832 MB/s
[exfat-nofuse]	1.2.9	1285 MB/s	1678 MB/s
exfat-fuse	N/A	751 MB/s	1464 MB/s
ext4	N/A	1283 MB/s	3356 MB/s

fio random I/O

Implementation	Base	Read	Write
exfat-linux	2.2.0	26 MB/s	1885 MB/s
[exfat-nofuse]	1.2.9	24 MB/s	1827 MB/s
exfat-fuse	N/A	1.6 MB/s	1.6 MB/s
ext4	N/A	29 MB/s	2821 MB/s

Mount options

• uid

• gid

• umask

• dmask

• fmask

• allow_utime

• iocharset

• quiet

• time_offset

  • Please refer to the vfat's documentation.

• errors=continue

  • Keep going on a filesystem error.

• errors=panic

  • Panic and halt the machine if an error occurs.

• errors=remount-ro

  • Remount the filesystem read-only on an error.

• discard

  • Enable the use of discard/TRIM commands to ensure flash storage doesn't run out of free blocks. This option may introduce latency penalty on file removal operations.

Enjoy!