What is Hackers' Pub?

Hackers' Pub is a place for software engineers to share their knowledge and experience with each other. It's also an ActivityPub-enabled social network, so you can follow your favorite hackers in the fediverse and get their latest posts in your feed.

0
0
0
0
0

If you wonder how this witchcraft is achieved:

disks are "hard sectored" more or less like older style hard disks and floppies were. This essentially turns the DVD-RAM disk into thousands of individually addressable "mini rewritable dvds"

The DVD drive can easily find the correct little bit of the disk to erase and overwrite.

This is how the disk can appear like any normal block device!

A really weird fact: DVD-RAM is predates DVD-RW or DVD+RW!

0
1
0
0
0
์–ด์ œ ์—„์ฒญ๋‚œ ์ง€์ถœ์„ ํ–ˆ์Šต๋‹ˆ๋‹ค. ์ด๊ฑฐ ๋‹ค ํ•ฉ์ณ์„œ 18๋งŒ์›...;;;;;
ๆ˜จๆ—ฅใฏใจใ‚“ใงใ‚‚ใชใ„ๅ‡บ่ฒปใ‚’ใ—ใพใ—ใŸใ€‚ใ“ใ‚Œๅ…จ้ƒจๅˆใ‚ใ›ใฆ2ไธ‡ๅ††โ€ฆ๏ผ›๏ผ›๏ผ›๏ผ›๏ผ›
1
1
0

ๅคšๆ‘ฉ็ธฃใฎ้ƒก้ƒจใ‚’็ดนไป‹ใ™ใ‚‹ใœ๏ผ
ๅ—ๅคšๆ‘ฉ้ƒกโ†’ใชใ‚“ใŸใพ๏ผ
่ฅฟๅคšๆ‘ฉ้ƒกโ†’ใซใ—ใŸใพ๏ผ
ๅŒ—ๅคšๆ‘ฉ้ƒกโ†’ใใŸใŸใพ๏ผ
่ฑŠๅคšๆ‘ฉ้ƒกโ†’ใจใ‚ˆใŸใพ๏ผ

0
0
0
0
1
1
1
0
0
1
0
1
1
1
1
0
1
0
0
0
0
0

ๆฑไบฌใชใ‚“ใ‚‚ใ‚ใ‹ใ‚‰ใ‚“ใ€‚ๅคšๆ‘ฉใƒ—ใƒฉใƒผใ‚ถใจใ‹ๅคšๆ‘ฉใ‚ปใƒณใ‚ฟใƒผใจใ‹ใŠใ‚‚ใ—ใ‚้ง…ๅใŒใ‚ใ‚‹ใใ‚‰ใ„ใ—ใ‹ใ‚ใ‹ใ‚‰ใ‚“

0

I just spent the entire morning debugging a MacOS sandboxing issue that turns out to have been "I said no to a permission prompt two days ago and this actually broke the entire VFS and I can't find where to reset it." Wowee mac dev.

0
0
0
0
1
1

anybody know how to tell what the *actual* checksum chosen by OpenZFS is, on FreeBSD?

When a zpool is created by bsdinstall, it defaults to checksum=on, and a micro benchmark is done to choose the appropriate checksum (from fletcher4, sha256, sha512, skein, blake3).

I would like to know what that chosen checksum is.

openzfs.github.io/openzfs-docs provides instructions for ZoL but its not matched on FreeBSD.
Sysctl shows only:

$ sysctl -a |egrep -i 'blake3|fletcher|sha2|sha5'
vfs.zfs.fletcher_4_impl: [fastest] scalar superscalar superscalar4 sse2 ssse3 avx2 avx512f avx512bw
vfs.zfs.sha512_impl: cycle [fastest] generic x64 avx avx2
vfs.zfs.sha256_impl: cycle [fastest] generic x64 ssse3 avx avx2 shani
vfs.zfs.blake3_impl: cycle [fastest] generic sse2 sse41 avx2 avx512

Which is not very helpful!

Inspecting zdb shows that the รผberblock uses fletcher4, if so that's a bad choice for almost all the machines I have, vs one of the more modern CPU-accelerated ones.

Uberblock:
magic = 0000000000bab10c
version = 5000
txg = 29818863
guid_sum = 12865431551488305392
timestamp = 1770722160 UTC = Tue Feb 10 11:16:00 2026
bp = DVA[0]=<0:1ef37817000:1000> DVA[1]=<0:1f26e5c1000:1000> DVA[2]=<0:8c341bf000:1000> [L0 DMU objset] fletcher4 uncompressed unencrypted LE contiguous unique triple size=1000L/1000P birth=29818863L/29818863P fill=75881 cksum=00000003035e0207:00000baf31d8f848:0016adf241101a15:1d6126f678dd7a91

0
0
0
0
0

ใ€Œใšใ‚‹ใ„ใ€ใง่กจ็พใ•ใ‚Œใฆใ„ใ‚‹ๆ„Ÿๆƒ…ใฎ9ๅ‰ฒใใ‚‰ใ„ใฏใ€Œ็พจใพใ—ใ„ใ€ใ ใจๆ€ใฃใฆใ„ใ‚‹

0
0
0
0
0

้›ป่ปŠไน—ใ‚ใ€œใจๆ€ใฃใŸใ‚‰ใŠ่ฒกๅธƒ่ฝใกใฆใŸใฎใง้ง…ๅ“กใ•ใ‚“ใซๅฑŠใ‘ใพใ—ใŸใ€€ๆœฌๆ—ฅใฎๅ–„่กŒใจใ„ใ†ใ“ใจใง

1
0
0

DNAMAG์€ ์ƒˆ๋กœ์šด ๊ฒƒ๋“ค์„ ๋””๊น…ํ•˜๊ณ 
์•„์นด์ด๋น™ํ•˜๋Š” ๋Œ€์ค‘๋ฌธํ™” ๋งค๊ฑฐ์ง„์ž…๋‹ˆ๋‹ค.

DNAMAG์€
์ธ์Šคํƒ€, ํŠธ์œ„ํ„ฐ, ๋ธ”๋ฃจ์Šค์นด์ด,
์Šค๋ ˆ๋“œ, ๋งˆ์Šคํ† ๋ˆ, ๋ฏธ์Šคํ‚ค ๋“ฑ์˜
ํ”Œ๋žซํผ์—์„œ ์—ฐ์žฌํ•˜๋ฉฐ

์œ ๋‹ˆ์Šค์ฟผ๋“œ๋ฅผ ํ†ตํ•ด
๋…์ž๋“ค๊ณผ ์•„์นด์ด๋น™ ํ•ฉ๋‹ˆ๋‹ค.

0

anybody know how to tell what the *actual* checksum chosen by OpenZFS is, on FreeBSD?

When a zpool is created by bsdinstall, it defaults to checksum=on, and a micro benchmark is done to choose the appropriate checksum (from fletcher4, sha256, sha512, skein, blake3).

I would like to know what that chosen checksum is.

openzfs.github.io/openzfs-docs provides instructions for ZoL but its not matched on FreeBSD.
Sysctl shows only:

$ sysctl -a |egrep -i 'blake3|fletcher|sha2|sha5'
vfs.zfs.fletcher_4_impl: [fastest] scalar superscalar superscalar4 sse2 ssse3 avx2 avx512f avx512bw
vfs.zfs.sha512_impl: cycle [fastest] generic x64 avx avx2
vfs.zfs.sha256_impl: cycle [fastest] generic x64 ssse3 avx avx2 shani
vfs.zfs.blake3_impl: cycle [fastest] generic sse2 sse41 avx2 avx512

Which is not very helpful!

Inspecting zdb shows that the รผberblock uses fletcher4, if so that's a bad choice for almost all the machines I have, vs one of the more modern CPU-accelerated ones.

Uberblock:
magic = 0000000000bab10c
version = 5000
txg = 29818863
guid_sum = 12865431551488305392
timestamp = 1770722160 UTC = Tue Feb 10 11:16:00 2026
bp = DVA[0]=<0:1ef37817000:1000> DVA[1]=<0:1f26e5c1000:1000> DVA[2]=<0:8c341bf000:1000> [L0 DMU objset] fletcher4 uncompressed unencrypted LE contiguous unique triple size=1000L/1000P birth=29818863L/29818863P fill=75881 cksum=00000003035e0207:00000baf31d8f848:0016adf241101a15:1d6126f678dd7a91

0
0