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Differential D20333

Make linux(4) create /dev/shm.
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Authored by trasz on May 21 2019, 12:29 PM.
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emaste
imp
kib

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tijl
dchagin
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rS354413: Make linux(4) create /dev/shm. Linux applications often expect
Summary

Make linux(4) create /dev/shm. Linux applications often expect
a tmpfs to be mounted there, and because they like to verify it's
actually a mountpoint, a symlink won't do.

Diff Detail

Repository
rS FreeBSD src repository - subversion
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Buildable 24360
Build 23182: arc lint + arc unit

Event Timeline

trasz created this revision.May 21 2019, 12:29 PM
Herald added a subscriber: imp. · View Herald TranscriptMay 21 2019, 12:29 PM
Harbormaster completed remote builds in B24356: Diff 57628.May 21 2019, 12:29 PM
dchagin added a comment.May 21 2019, 2:00 PM

linux_common is not used in i386

dchagin added a comment.May 21 2019, 2:03 PM

I would prefer put common code to the compat/linux/linux.c and put linux_dev_shm_destroy/linux_dev_shm_create decl to the linux.h

trasz updated this revision to Diff 57633.May 21 2019, 3:11 PM

Move stuff around.

Harbormaster completed remote builds in B24360: Diff 57633.May 21 2019, 3:11 PM
trasz added a comment.May 21 2019, 3:12 PM
In D20333#438430, @dchagin wrote:

linux_common is not used in i386

What do you mean? Or, ask another way, where should I call it from to make it work for i386?

dchagin added a comment.May 21 2019, 3:44 PM
In D20333#438435, @trasz wrote:
In D20333#438430, @dchagin wrote:

linux_common is not used in i386

What do you mean? Or, ask another way, where should I call it from to make it work for i386?

in linux_elf_modevent() in i386/linux/linux_sysvec.c

trasz updated this revision to Diff 57758.May 23 2019, 12:22 PM

Also call stuff for i386.

Harbormaster completed remote builds in B24421: Diff 57758.May 23 2019, 12:22 PM
dchagin accepted this revision.May 23 2019, 6:55 PM
This revision is now accepted and ready to land.May 23 2019, 6:55 PM
tijl added a comment.May 24 2019, 8:21 AM

Please also bump OSVERSION so the creation of /compat/linux/dev/shm can be made conditional in emulators/linux_base-c[67]

dchagin added a comment.May 24 2019, 2:22 PM

as far as I understand we can create /dev/fd same way?

trasz added a comment.May 25 2019, 7:40 PM

This is a bit hacky, even for my standards, so I've come up with this as an alternative: https://reviews.freebsd.org/D20411.

trasz mentioned this in D20411: Add devfs(5) support for VOP_MKDIR(9) and VOP_RMDIR(9).Oct 1 2019, 11:52 AM
emaste added a subscriber: emaste.Oct 24 2019, 2:30 PM

I have no objection

emaste added a comment.Oct 24 2019, 2:43 PM

I have no objection

Further, I am not familiar enough with the devfs machinery to effectively review (previously I would not have suspected make_dev as the way to create a devfs directory), but I support the intent / effect of this change.

kib added a subscriber: kib.Oct 24 2019, 2:53 PM
kib added inline comments.
sys/compat/linux/linux.c
538

I suggest "shm/.placeholder" or "shm/.dummy". Might also make sense to change mode to 0.

540

\n at the EoL

emaste added inline comments.Oct 24 2019, 3:59 PM
sys/compat/linux/linux.c
538

Ah I see now. What about shm/.mountpoint in that case?

trasz updated this revision to Diff 63735.Oct 28 2019, 9:16 PM

Apply comments from kib@ and emaste@.

This revision now requires review to proceed.Oct 28 2019, 9:16 PM
Harbormaster completed remote builds in B27245: Diff 63735.Oct 28 2019, 9:16 PM
trasz marked 3 inline comments as done.Oct 28 2019, 9:19 PM
kib added inline comments.Oct 29 2019, 8:07 AM
sys/i386/linux/linux_sysvec.c
1009 ↗(On Diff #63735)

So if both 64 and 32bit linix.ko are loaded, one of them would print an error. If another one is unloaded before the module that printed an error, the node is destroyed. Which raises the next question, did you actually tried it ? I wonder what happens to the system when devfs directory goes away while being used as mount point (I have no idea and curious).

trasz added a comment.Oct 29 2019, 10:29 AM

Well, they don't print an error. I'm not quite sure why, but I've tested both scenarios - kldloading linux.ko and then linux64.ko, and the other way around; same with kldunloading.

As for what happens when the devfs goes away - you're left with a mount point that's not accessible with full path. You can unmount it just fine, though. And we depend on that behaviour for reroot.

kib added a comment.Oct 29 2019, 3:05 PM
In D20333#484711, @trasz wrote:

Well, they don't print an error. I'm not quite sure why, but I've tested both scenarios - kldloading linux.ko and then linux64.ko, and the other way around; same with kldunloading.

Then there must be a bug either in the testing methodology or in the code, right ? Ensure that the make_dev line is executed in both cases.

trasz added a comment.Oct 30 2019, 9:39 PM
In D20333#484720, @kib wrote:
In D20333#484711, @trasz wrote:

Well, they don't print an error. I'm not quite sure why, but I've tested both scenarios - kldloading linux.ko and then linux64.ko, and the other way around; same with kldunloading.

Then there must be a bug either in the testing methodology or in the code, right ? Ensure that the make_dev line is executed in both cases.

I'm not sure how it works, but there seems to be some magic that makes sure it gets called in the right circumstances. Existing code already depends on it - eg linux_osd_jail_register() is called in the exact same way.

tijl added a comment.Oct 31 2019, 9:32 AM

On amd64 the code is in linux_common.ko, not linux.ko and linux64.ko. So the directory is created/destroyed when linux_common is loaded/unloaded.

This revision was not accepted when it landed; it landed in state Needs Review.Nov 6 2019, 8:53 PM
Closed by commit rS354413: Make linux(4) create /dev/shm. Linux applications often expect (authored by trasz). · Explain Why
This revision was automatically updated to reflect the committed changes.
trasz added a commit: rS354413: Make linux(4) create /dev/shm. Linux applications often expect.

Revision Contents
Changeset List

PathSize
sys/
compat/
linux/
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27 lines
4 lines

Diff 57633

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sys/compat/linux/linux.h

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sys/compat/linux/linux.c

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sys/compat/linux/linux_common.c

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