Using FAT32 long file names on NuttX

NuttX supports FAT32 with long file names, but there is some details that you need to know to get it working. I will share here the issues that I was facing and how I fixed it.

The original FAT uses 8.3 (8 chars for name and 3 chars for extension), but it can supports files with up to 255 characters (including the extension).

To use it we need to enable long file name support in the menuconfig:

 File Systems  --->
     [*] FAT file system
     [*]   FAT upper/lower names
     [*]   FAT long file names             -------->  (CONFIG_FAT_LFN=y)
     (255)   FAT maximum file name size    -------->  (CONFIG_FAT_MAXFNAME=255)

Initially I will mount an empty SDCard to do my tests:

NuttShell (NSH)

nsh> mount -t vfat /dev/mmcsd0 /mnt

nsh> ls /mnt
/mnt:

nsh>

Let’s to create a small 8.3 file that will be renamed:

nsh> echo "Small file" > /mnt/tinyfile.txt
nsh> ls -l /mnt/tinyfile.txt
 -rw-rw-rw-      12 /mnt/tinyfile.txt
nsh>

Now I will try to rename it to a file with a long name:

nsh> mv /mnt/tinyfile.txt /mnt/this_is_a_file_with_a_long_name_jnsh>

Strange, while I was typing “this_is_a_file_with_a_long_name_just_for_test.txt” the typing was interrupted and the nsh> appeared.

Let see if the file was renamed:

nsh> ls /mnt
/mnt:
 this_is_a_file_with_a_long_name_

Then I remembered that the max line size of NSH was just 60 (CONFIG_NSH_LINELEN=60), I will increase it to 300 characters:

Application Configuration  --->
    NSH Library  --->
          Command Line Configuration  --->
              (300) Max command line length    -------->  (CONFIG_NSH_LINELEN=300)

I will create a tinyfile.txt again and try to rename it:

nsh> mv /mnt/tinyfile.txt /mnt/this_is_a_file_with_a_long_name_just_for_test.txt
nsh> 

Right, now the nsh prompt accept the enter the name, but let see if the file was created correctly:

nsh> ls /mnt
/mnt:
 this_is_a_file_with_a_long_name_
 this_is_a_file_with_a_long_name_

Whoa, it created two files with same name? How it is possible? Don’t worry, these files are different. Opening the SDCard in the Linux I can see:

this_is_a_file_with_a_long_name_j
this_is_a_file_with_a_long_name_just_for_test.txt

So, the LS command is showing only 32 characters. After some investigation I discovered that CONFIG_NAME_MAX=32 was the issue. Let to increase it to 255:

RTOS Features  --->
    Files and I/O  --->
        (255) Maximum size of a file name    -------->  (CONFIG_NAME_MAX=255)

Now I can see the files:

nsh> ls /mnt
/mnt:
 this_is_a_file_with_a_long_name_j
 this_is_a_file_with_a_long_name_just_for_test.txt

My next step is to create a file with 255 characters, like this:

this_file_will_have_a_big_filename_to_verify_how_to_work_with_files_with_long_names_our_test_need_to_have_the_max_filename_size_supported_by_fat32_that_means_it_could_have_up_to_255_characters_including_the_extension_in_the_filename_so_here_we_arrived.txt

nsh> echo "Test" > /mnt/this_file_will_have_a_big_filename_to_verify_how_to_work_with_files_with_long_names_our_test_need_to_have_the_max_filename_size_supported_by_fat32_that_means_it_could_have_up_to_255_characters_including_the_extension_in_the_filename_so_here_we_arrived.txt
nsh> ls /mnt
/mnt:
 this_file_will_have_a_big_filename_to_verify_how_to_work_with_files_with_long_names_our_test_need_to_have_the_max_filename_size_supported_by_fat32_that_means_it_could_have_up_to_255_characters_including_the_extension_in_the_filename_so_here_we_arrived.txt
nsh> 

Very nice! It worked correctly.

As you can see NuttX is similar to Linux kernel, many features depends on other features’ configuration. They are inter-dependent.