Overwriting relative symlink leads to undesirable behavior. Consider the following example:

# Create some directories

mkdir test

mkdir test/folder1

mkdir test/folder2

#Create some files

touch test/folder1/file1

touch test/folder1/file2

#Create a relative symlink in folder2 to file1

ln -sr test/folder1/file1 test/folder2/link

#Check the link

ls -l test/folder2/link

# Correctly output a link to ../folder1/file1

#Overwrite the symlink to point to file2

ln -sfr test/folder1/file2 test/folder2/link

#Check the link

ls -l test/folder2/link

# Wrongly output a link to file2 instead of ../folder1/file2

This undesirable behavior is due to a dereferencing of the target when the relative path is computed. Passing CAN_NOLINKS flag to canonicalize_filename_mode solves the problem.