On 2/25/21 6:56 PM, John Reiser wrote:
>> Tools such as ls or stat report the size of a directory. Of course it is not
>> the content size.
>> stat -c %s /home/sergio/.config
>> 6550
>>
>> What does 6550 mean in btrfs context?
>
> Regardless of filesystem type, the size of a directory is the sum of the sizes
> of the struct linux_dirent (or linux_dirent64) for the filenames of the
> contained files.
> See the manual page "man 2 getdents".
That's not correct; dirents are in-memory structures, unrelated
to what the [fl]stat(2) interface used by ls returns for a directory.
The size returned by stat(2) (aka ls) of a directory inode is
filesystem implementation dependent, and AFAIK has no well-defined
meaning. stat(2) refers to st_size only for files and symlinks,
not for directories. Same w/ POSIX:
off_t st_size For regular files, the file size in bytes.
For symbolic links, the length in bytes of the
pathname contained in the symbolic link.
So, as one example on ext4 - directories never shrink.
# mkdir dir
# ls -ld dir
drwxr-xr-x. 2 root root 4096 Feb 26 00:48 dir
# touch dir/123456789
# ls -ld dir
drwxr-xr-x. 2 root root 4096 Feb 26 01:00 dir
# for I in `seq 1 2000`; do touch dir/longfilename$I; done
# ls -ld dir
drwxr-xr-x. 2 root root 69632 Feb 26 00:49 dir
# rm -f dir/*
# ls -ld dir
drwxr-xr-x. 2 root root 69632 Feb 26 00:49 dir
69632 byte directory with no files in it, wheeee.
xfs is different:
# mkdir dir
# ls -ld dir
drwxr-xr-x. 2 root root 6 Feb 26 00:58 dir
# touch dir/123456789
# ls -ld dir
drwxr-xr-x. 2 root root 23 Feb 26 00:59 dir
# for I in `seq 1 2000`; do touch dir/longfilename$I; done
# ls -ld dir
drwxr-xr-x. 2 root root 65536 Feb 26 00:59 dir
# rm -f dir/*
# ls -ld dir
drwxr-xr-x. 2 root root 6 Feb 26 00:59 dir
btrfs is still different:
# mkdir dir
# ls -ld dir
drwxr-xr-x. 1 root root 0 Feb 26 01:05 dir
# touch dir/123456789
# ls -ld dir
drwxr-xr-x. 1 root root 18 Feb 26 01:06 dir
# for I in `seq 1 2000`; do touch dir/longfilename$I; done
# ls -ld dir
drwxr-xr-x. 1 root root 61804 Feb 26 01:06 dir
# rm -f dir/*
# ls -ld dir
drwxr-xr-x. 1 root root 0 Feb 26 01:06 dir
In short, "size" of a dir doesn't tell you much.
-Eric
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