Change #254705

Comments

readlink,realpath: promptly diagnose write errors
The 'readlink' and 'realpath' programs have an uncommon case where they
can run for a very long time. When canonicalizing file names longer than
PATH_MAX, we have to call 'openat' for each directory up the tree until
we reach root which takes a long time. Here is an example of the current
behavior:

    $ mkdir -p $(yes a/ | head -n $((32 * 1024)) | tr -d '\n')
    $ while cd $(yes a/ | head -n 1024 | tr -d '\n'); do :; \
        done 2>/dev/null
    $ pwd | tr '/' '\n' | wc -l
    32771
    $ env time --format=%E readlink -f $(yes . | head -n 5) > /dev/full
    readlink: write error: No space left on device
    Command exited with non-zero status 1
    0:59.72
    $ env time --format=%E realpath $(yes . | head -n 5) > /dev/full
    realpath: write error: No space left on device
    Command exited with non-zero status 1
    1:00.32

It is better to exit as soon as there is an error writing to standard
output:

    $ env time --format=%E readlink -f $(yes . | head -n 5) > /dev/full
    readlink: write error: No space left on device
    Command exited with non-zero status 1
    0:11.88
    $ env time --format=%E realpath $(yes . | head -n 5) > /dev/full
    realpath: write error: No space left on device
    Command exited with non-zero status 1
    0:12.04

* src/readlink.c (main): Check if standard output has it's error flag
set after printing a file name.
* src/realpath.c (process_path): Likewise.
* NEWS: Mention the improvement.

Changed files

• NEWS
• src/readlink.c
• src/realpath.c