#1039042 - coreutils: tail: on blockdevs reads the whole thing, doesn't on files of the same size

Debian Bug report logs - #1039042
coreutils: tail: on blockdevs reads the whole thing, doesn't on files of the same size

Reported by: наб <[email protected]>

Date: Sat, 24 Jun 2023 23:21:02 UTC

Severity: normal

Found in version coreutils/9.1-1

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Date: Sun, 25 Jun 2023 01:17:10 +0200
From: наб <[email protected]>
To: Debian Bug Tracking System <[email protected]>
Subject: coreutils: tail: on blockdevs reads the whole thing, doesn't on
 files of the same size
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Package: coreutils Version: 9.1-1 Severity: normal Dear Maintainer, $ cp --sparse=always /dev/zvol/filling/store/nabijaczleweli/vm-zoot /tmp/ $ time tail /dev/zvol/filling/store/nabijaczleweli/vm-zoot | b2sum 11d28bd10ad4d4ae652e02aaaa6f59f1ef5ff5f44111e3e3c80d5ae01f666e00f38d626784539b9f095255a246d9b6b56624fd08c8916a10b16e7b5b6560d7f1 - real 0m17.235s user 0m1.344s sys 0m9.693s $ time tail /tmp/vm-zoot | b2sum 11d28bd10ad4d4ae652e02aaaa6f59f1ef5ff5f44111e3e3c80d5ae01f666e00f38d626784539b9f095255a246d9b6b56624fd08c8916a10b16e7b5b6560d7f1 - real 0m0.005s user 0m0.005s sys 0m0.004s $ time cat /dev/zvol/filling/store/nabijaczleweli/vm-zoot | tail | b2sum 11d28bd10ad4d4ae652e02aaaa6f59f1ef5ff5f44111e3e3c80d5ae01f666e00f38d626784539b9f095255a246d9b6b56624fd08c8916a10b16e7b5b6560d7f1 - real 0m17.271s user 0m1.620s sys 0m17.504s Somehow I feel there's no reason that tail couldn't lseek(SEEK_END) on a blockdev just as well as it can do on a regular file. Best, наб -- System Information: Debian Release: 12.0 APT prefers stable-security APT policy: (500, 'stable-security'), (500, 'stable-debug'), (500, 'stable') Architecture: amd64 (x86_64) Foreign Architectures: i386 Kernel: Linux 6.1.0-9-amd64 (SMP w/24 CPU threads; PREEMPT) Kernel taint flags: TAINT_PROPRIETARY_MODULE, TAINT_FIRMWARE_WORKAROUND, TAINT_OOT_MODULE, TAINT_UNSIGNED_MODULE Locale: LANG=en_GB.UTF-8, LC_CTYPE=en_GB.UTF-8 (charmap=UTF-8), LANGUAGE=en_GB:en Shell: /bin/sh linked to /usr/bin/dash Init: systemd (via /run/systemd/system) LSM: AppArmor: enabled Versions of packages coreutils depends on: ii libacl1 2.3.1-3 ii libattr1 1:2.5.1-4 ii libc6 2.36-9 ii libgmp10 2:6.2.1+dfsg1-1.1 ii libselinux1 3.4-1+b6 coreutils recommends no packages. coreutils suggests no packages. -- no debconf information

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Debian Bug report logs - #1039042 coreutils: tail: on blockdevs reads the whole thing, doesn't on files of the same size

Debian Bug report logs - #1039042
coreutils: tail: on blockdevs reads the whole thing, doesn't on files of the same size