-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 6/10/15 7:10 PM, Hugo Mills wrote: > On Tue, Jun 09, 2015 at 07:55:05PM +0200, pubny@xxxxxxxxx wrote: >> Hi, >> >> I've noticed this "@" sign in the subvolume's path with SLES12. >> I'm wondering what is its purpose. openSUSE 13.2 doesn't seem to >> be using it. > > They created a subvolume called "@" and then put all the other > subvolumes under there. There's nothing special about it. > > The @ is often used as a prefix on subvolumes (e.g. in Ubuntu) to > indicate that they're subvolumes, but it's not required, and > doesn't have any extra meaning beyond being a useful naming > convention. Yep. That explanation is accurate but is missing the rest of the story. The choice of @ is probably due to following the convention started by the Ubuntu folks but also because it's the least complicated of the alternative names we could have used. The @ subvolume is set as the default subvolume. As you'd expect, it's mounted at / and used as such. The reason we use a separate subvolume is so we can easily implement our boot-and-rollback-from-snapshot functionality in SLE12. Having the root file system as a separate subvolume means we can move one of the snapshot subvolumes into the fs tree root, move the other @ subvolumes into that subvolume, and we have a rolled back system from which we can easily remove the now-unused root. If we didn't use a separate subvolume for it, it would make the rollback very complicated. It's used in concert with our GRUB implementation that iterates and presents possible snapshots to use as a root file system in lieu of the "real" one should a problem occur. - -Jeff >> >> SLES12: # btrfs sub list / ID 257 gen 2270 top level 5 path @ ID >> 258 gen 1655 top level 257 path @/boot/grub2/i386-pc ID 259 gen >> 4263 top level 257 path @/boot/grub2/x86_64-efi ID 260 gen 4037 >> top level 257 path @/opt ID 261 gen 2553 top level 257 path >> @/srv ID 262 gen 4521 top level 257 path @/tmp ID 263 gen 4492 >> top level 257 path @/usr/local ID 264 gen 1655 top level 257 path >> @/var/crash ID 265 gen 1655 top level 257 path @/var/lib/mailman >> ID 266 gen 1655 top level 257 path @/var/lib/named ID 267 gen >> 1655 top level 257 path @/var/lib/pgsql ID 268 gen 4523 top level >> 257 path @/var/log ID 269 gen 1655 top level 257 path @/var/opt >> ID 270 gen 4524 top level 257 path @/var/spool ID 271 gen 4521 >> top level 257 path @/var/tmp ID 275 gen 4505 top level 257 path >> @/.snapshots >> >> >> openSUSE 13.2: >> >> # btrfs subvol list / ID 257 gen 3481911 top level 5 path >> boot/grub2/i386-pc ID 258 gen 3481911 top level 5 path >> boot/grub2/x86_64-efi ID 259 gen 3517714 top level 5 path home ID >> 260 gen 3515789 top level 5 path opt ID 261 gen 3513493 top level >> 5 path srv ID 262 gen 3513372 top level 5 path tmp ID 263 gen >> 3517660 top level 5 path usr/local ID 264 gen 3513372 top level 5 >> path var/crash ID 265 gen 3513372 top level 5 path >> var/lib/mailman ID 266 gen 3513372 top level 5 path >> var/lib/named ID 267 gen 3513372 top level 5 path var/lib/pgsql >> ID 268 gen 3517714 top level 5 path var/log ID 269 gen 3513372 >> top level 5 path var/opt ID 270 gen 3517714 top level 5 path >> var/spool ID 271 gen 3517706 top level 5 path var/tmp ID 276 gen >> 3517669 top level 5 path .snapshots > - -- Jeff Mahoney SUSE Labs -----BEGIN PGP SIGNATURE----- Version: GnuPG/MacGPG2 v2.0.19 (Darwin) iQIcBAEBAgAGBQJVeOlbAAoJEB57S2MheeWy0JYP/1mbM5ybHNcwEB21CbS+5ujv omBmiVhX6nAcTDAJ2OJG7MsrE4L1j93R8gv/xRkPjBLuaiqJ+wr88VaG/AcKvtSZ qMF64PJCNzsXFd0FFPi8CNXxhVbJyEKF+m8Xl+tfRsMhsNIKdbqkMHInMc99qWJH dMLTSYObvdo9AYIkOj8PM6nBjeQ4zEBQY9uOf9M9HL8Ulc1VQgzSu1giuvHg8/Cf Ela2iZJi2APZeNisQtQcJssMyBaDTbSH0RhQh8kcdfG6GCruSDR8AWbyuY36OeaG 5Ifp4J7oSS+eUwlTtvLFfZl079VmJWZbF/KEy8GfY++kp+BVB95Z8QOKVOVTEA8A 4AvkMfdGvtykZJNRskXGaIsUIX07iTmT2f+VyN7jbfp2J5FyBALp+i4Ub5fyjUZG +OWcAIkTC9z2AQW77ZMdA4DdkHk5bi3aRSCNV1gSPGDib5CH5ZLyMY/KKtxCLSnO syNdcZmQs4bb7FZBfcM4CQraUYsnBl4ArGechkMWpJCrMx2dtRrGlKlh+7KmG+m8 60xBKU3ApmZrcKUTAcWvN2cy72xmc8GZaOPnNepAUhMLduarsEtyCemOkGCZxRiu c0QRGhGBgK91MBF1KxXzrnO0cm1ijdjMAbwmol6vEYRzXItXK3AeD74IeY6Abqr/ U2lTFYlKYpkTmzhk0gM8 =lO/K -----END PGP SIGNATURE----- -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
