mount points are not extracted in sequential read mode

Consider an archive created as follows:
$ dar -c /mnt/a -R / -M -D

Assuming that / and /mnt are distinct mounted filesystems, mount points
(e.g. /proc, /sys, etc.) will be saved correctly as empty directories
due to -M and -D.

When extracting normally (i.e. random I/O), these mount points are
restored correctly as empty directories:
$ dar -x /mnt/a

In sequential read mode, they are not extracted at all (unexpected):
$ dar -x - -0 < /mnt/a.1.dar

I notice that the man page notes some limitations about sequential read
mode but none of them seem related to this case.  I'm guessing this is
a bug; i.e. either these empty directories should be extracted in
sequential read mode just as they would be in "random I/O" mode, or at
least a warning should be issued indicating that they've been skipped.

Sincerest apologies if I have overlooked something reasonably obvious.

I have attached a shell script to demonstrate.

usage:  dar-test.sh [noclean]

Please note the following:
1)  sudo is called to mount/unmount a 1MiB tmpfs filesystem
2a)  When arg 1 is noclean:  the script will echo "cleanup" commands
instead of executing them.
2b)  Otherwise, the script will execute cleanup commands which includes
!!!! rm -fr !!!!

To be on the safe side, I recommend running in a "scratch" environment.

Below is a transcript from running this script on my host:
$ ./dar-test.sh 
Warning: using insecure memory!

 dar version 2.6.3, Copyright (C) 2002-2019 Denis Corbin
   Long options support         : YES

 Using libdar 6.1.0 built with compilation time options:
   Libz compression (gzip)      : YES
   Libbz2 compression (bzip2)   : YES
   Liblzo2 compression (lzo)    : YES
   Liblzma compression (xz)     : YES
   Strong encryption (libgcrypt): YES
   Public key ciphers (gpgme)   : NO
   Extended Attributes support  : YES
   Large files support (> 2GB)  : YES
   ext2fs NODUMP flag support   : YES
   Integer size used            : 64 bits
   Thread safe support          : YES
   Furtive read mode support    : YES
   Linux ext2/3/4 FSA support   : YES
   Mac OS X HFS+ FSA support    : NO
   Detected system/CPU endian   : little
   Posix fadvise support        : YES
   Large dir. speed optimi.     : YES
   Timestamp read accuracy      : 1 microsecond
   Timestamp write accuracy     : 1 microsecond
   Restores dates of symlinks   : YES
   Multiple threads (libthreads): NO 
   Delta compression support    : NO
   Remote repository support    : NO

 compiled the Apr  1 2019 with GNUC version 9.0.1 20190312 (Red Hat
9.0.1-0.10)
 dar is part of the Disk ARchive suite (Release 2.6.3)
 dar comes with ABSOLUTELY NO WARRANTY; for details
 type `dar -W'. This is free software, and you are welcome
 to redistribute it under certain conditions; type `dar -L | more'
 for details.

mkdir: created directory '/tmp/tmp.562G7984gj/fs-root'
mkdir: created directory '/tmp/tmp.562G7984gj/extract'
mkdir: created directory '/tmp/tmp.562G7984gj/extract-sequential'
mount: none mounted on /tmp/tmp.562G7984gj/fs-root/z.
>>>> BEGIN: dar --create /tmp/tmp.562G7984gj/a --fs-root
/tmp/tmp.562G7984gj/fs-root -M -D -v
Warning: using insecure memory!
Creating low layer: Writing archive into a plain file object...
Writing down the archive header...
Adding a new layer on top: Caching layer for better performances...
Adding a new layer on top: Escape layer to allow sequential reading...
All layers have been created successfully
Building the catalog object...
Processing files for backup...
Furtive read mode requires either root permission and FOWNER
capability, falling back to normal filesystem read
Adding file to archive: /tmp/tmp.562G7984gj/fs-root/a
building delta signature with block size of 2048 bytes
Saving Extended Attributes for /tmp/tmp.562G7984gj/fs-root/a
Writing down archive contents...
Closing the escape layer...
Writing down the first archive terminator...
Writing down archive trailer...
Writing down the second archive terminator...
Closing archive low layer...
Archive is closed.


 --------------------------------------------
 1 inode(s) saved
   including 0 hard link(s) treated
 0 inode(s) changed at the moment of the backup and could not be saved
properly
 0 byte(s) have been wasted in the archive to resave changing files
 0 inode(s) with only metadata changed
 0 inode(s) not saved (no inode/file change)
 0 inode(s) failed to be saved (filesystem error)
 1 inode(s) ignored (excluded by filters)
 0 inode(s) recorded as deleted from reference backup
 --------------------------------------------
 Total number of inode(s) considered: 2
 --------------------------------------------
 EA saved for 1 inode(s)
 FSA saved for 0 inode(s)
 --------------------------------------------
Making room in memory (releasing memory used by archive of
reference)...
Final memory cleanup...
>>>> END: dar --create /tmp/tmp.562G7984gj/a --fs-root
/tmp/tmp.562G7984gj/fs-root -M -D -v
>>>> BEGIN: dar --extract /tmp/tmp.562G7984gj/a -v
Warning: using insecure memory!
Opening archive a ...
Opening the archive using the multi-slice abstraction layer...
Reading the archive trailer...
Opening construction layer...
Considering cyphering layer...
No cyphering layer opened
Opening escape sequence abstraction layer...
Opening the compression abstraction layer (compression algorithm used
is none)...
All layers have been created successfully
Loading catalogue into memory...
Locating archive contents...
Reading archive contents...
Restoring file's data: /tmp/tmp.562G7984gj/extract/z
/tmp/tmp.562G7984gj/extract/zCould not restore original file ownership:
Operation not permitted
Restoring file's data: /tmp/tmp.562G7984gj/extract/a
Restoring file's EA: /tmp/tmp.562G7984gj/extract/a


 --------------------------------------------
 2 inode(s) restored
    including 0 hard link(s)
 0 inode(s) not restored (not saved in archive)
 0 inode(s) not restored (overwriting policy decision)
 0 inode(s) ignored (excluded by filters)
 0 inode(s) failed to restore (filesystem error)
 0 inode(s) deleted
 --------------------------------------------
 Total number of inode(s) considered: 2
 --------------------------------------------
 EA restored for 1 inode(s)
 FSA restored for 0 inode(s)
 --------------------------------------------
Final memory cleanup...
>>>> END: dar --extract /tmp/tmp.562G7984gj/a -v
>>>> BEGIN: dar --extract - -0 -v
Warning: using insecure memory!
Opening archive - ...
Opening standard input to read the archive...
Reading the archive header...
Considering cyphering layer...
No cyphering layer opened
Opening escape sequence abstraction layer...
Opening the compression abstraction layer (compression algorithm used
is none)...
All layers have been created successfully
The catalogue will be filled while sequentially reading the archive,
preparing the data structure...
Restoring file's data: /tmp/tmp.562G7984gj/extract-sequential/a
Restoring file's EA: /tmp/tmp.562G7984gj/extract-sequential/a


 --------------------------------------------
 1 inode(s) restored
    including 0 hard link(s)
 0 inode(s) not restored (not saved in archive)
 0 inode(s) not restored (overwriting policy decision)
 0 inode(s) ignored (excluded by filters)
 0 inode(s) failed to restore (filesystem error)
 0 inode(s) deleted
 --------------------------------------------
 Total number of inode(s) considered: 1
 --------------------------------------------
 EA restored for 1 inode(s)
 FSA restored for 0 inode(s)
 --------------------------------------------
Final memory cleanup...
>>>> END: dar --extract - -0 -v
/tmp/tmp.562G7984gj/extract/:
a  z

/tmp/tmp.562G7984gj/extract-sequential/:
a
umount: /tmp/tmp.562G7984gj/fs-root/z unmounted
removed '/tmp/tmp.562G7984gj/a.1.dar'
removed '/tmp/tmp.562G7984gj/extract-sequential/a'
removed directory '/tmp/tmp.562G7984gj/extract-sequential'
removed '/tmp/tmp.562G7984gj/extract/a'
removed directory '/tmp/tmp.562G7984gj/extract/z'
removed directory '/tmp/tmp.562G7984gj/extract'
removed directory '/tmp/tmp.562G7984gj/fs-root/z'
removed '/tmp/tmp.562G7984gj/fs-root/a'
removed directory '/tmp/tmp.562G7984gj/fs-root'
removed directory '/tmp/tmp.562G7984gj'

_______________________________________________
Dar-support mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/dar-support

#!/bin/bash
set -o nounset -o errexit

debug() {
    echo ">>>> BEGIN: $@"
    "$@"
    echo ">>>> END: $@"
}

exitHandlers=()
handlerCmdPrefix=
if [[ ${1-} == noclean ]] ; then handlerCmdPrefix=echo ; fi
onExit() {
    local i=${#exitHandlers[*]}
    if [[ $i -gt 0 && $handlerCmdPrefix == echo ]] ; then
        echo '!!!! Please run the following commands to clean up !!!!' >&2
    fi
    while [[ $i -gt 0 ]] ; do
        "${exitHandlers[$((--i))]}" $handlerCmdPrefix
    done
}
trap onExit EXIT

dar --version

root=$(mktemp -d)
exitRm() { "$@" rm -vfr -- "${root}" ; }
exitHandlers+=(exitRm)

mkdir -v -- "${root}"/{fs-root,extract{,-sequential}}
touch -- "${root}/fs-root/a"
mkdir -- "${root}/fs-root/z"

sudo mount -v -t tmpfs -o size=1m none "${root}/fs-root/z"
exitUnmount() { "$@" sudo umount -v -- "${root}/fs-root/z" ; }
exitHandlers+=(exitUnmount)

debug dar --create "${root}/a" --fs-root "${root}/fs-root" -M -D -v

( cd -- "${root}/extract" &&
    debug dar --extract "${root}/a" -v )
( cd -- "${root}/extract-sequential" &&
    debug dar --extract - -0 -v < "${root}/a.1.dar" )

ls -- "${root}/extract"{,-sequential}/