OpenAFS Native Mountpoints on Linux Andrew Deason June 2019 - - PowerPoint PPT Presentation

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Jan 08, 2023 577 likes •749 views

OpenAFS Native Mountpoints on Linux Andrew Deason June 2019 OpenAFS Workshop 2019 1 Background Single mountpoints are pretty simple: 2 Background What about multiple mountpoints? What is ..? 3 Dentries and Inodes Inodes:

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OpenAFS Native Mountpoints on Linux

Andrew Deason June 2019

OpenAFS Workshop 2019 1

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Background

Single mountpoints are pretty simple:

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Background

What about multiple mountpoints? What is ‘..’?

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Dentries and Inodes

Inodes: files, dentries: links
No directory hard-links
Why?
Historically, AFS mountpoints were dir-links
or ‘..’ moved on access

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Dir-link workarounds

What about /proc/$pid/cwd, /proc/$pid/fd/$n?

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Dir-link workarounds

d_automount, follow_link
Commit: “Make dir dentry aliases act like symlinks”
https://gerrit.openafs.org/7741
find
./mtpt1 → ./mtpt1/subdir → ./mtpt1/subdir/mtpt2 →

./mtpt1/subdir/mtpt2/.. → ./

There must be a better way!

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Real Mountpoints

Linux VFS says: must use real mounts
volumes/mtpts fit the model
Why don’t we already have it?
userspace: mount
kernel: GPLONLY vfs_kern_mount()

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Non-GPL In-kernel Mounts

Alternatives:
GPL wrapper
FUSE
kAFS
Userspace upcall
Existing upcalls:
DNS (AFSDB)
OS X mv helper

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Linux Native Mounts

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Linux Native Mounts

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Linux Native Mounts

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Concerns

MNT_EXPIRE in a loop
10k mounts, 100k, . . . ?
Needs testing

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Future

/afs/:.mount/cell:vol:vnode:uniq
Non-/afs mountpoints
Separate devices
df -h

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Code

Top commit https://gerrit.openafs.org/13285 All commits https://gerrit.openafs.org/#/q/topic:linux-native-mounts Slides http://dson.org/talks

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