Question on FileETag and mod_dav_fs

[Tianyin Xu <tixu@xxxxxxxxxxx>]

Hi, all,

I saw the warning message in the manual, the FileETag entry:

-------------------------------------------------------------

Warning

    Do not change the default for directories or locations that have WebDAV
    enabled and use mod_dav_fs as a storage provider.
    mod_dav_fs uses MTime Size
    as a fixed format for ETag comparisons on conditional requests.
    These conditional requests will break if the ETag format is
    changed via FileETag.
    

-------------------------------------------------------------

I do not get it. What will happen when I use WebDAV with mod_dav_fs while setting FileETag as None? 

According to the source code point of view, it seems that there's some relation between dav_fs_getetag() in repos.c and ap_make_etag() in http_etag.c. 

Could some one explain a little bit to me?

Thank you so much!!!
Tianyin