nullfs: add nounixbypass mount option

[kib]

Summary

nullfs: add nounp_bypass mount option

The option, when set, disables bypassing the unix socket vnode down
to the lower mp, effectively preventing connection to nullfs unix
socket from being acceptable from the lower mp (and vice versa).

This is done by providing a vop vector that stops bypass for unp-related
VOPs.  I believe that VFS_VOP_VECTOR_REGISTER() does the right thing
there regardless of the order of initialization.


nullfs_mount: use symbols instead of string literals for cache mount options


nullfs: add helper testing for vnode belonging to nullfs mount


fs/nullfs/null.h: put first definition after headers include

[markj]

This should be documented in mount_nullfs.8. The implementation looks ok to me.

The name sounds a bit strange to me. The mount_nullfs terminology explains what "bypass" means, but it's still a bit unclear IMO. What do you think about unix_private, nounix_private?

[kib]

In D52983#1210802, @markj wrote:

This should be documented in mount_nullfs.8. The implementation looks ok to me.

I will after the patch is finalized.

The name sounds a bit strange to me. The mount_nullfs terminology explains what "bypass" means, but it's still a bit unclear IMO. What do you think about unix_private, nounix_private?

For me, 'private' is worse. What exactly is the scope where the socket becomes private? People would think about jails or whatever namespace restriction they intend, but not the pass from upper to lower.
I can rename user-visible option to unixbypass e.g.

[markj]

In D52983#1210842, @kib wrote:

In D52983#1210802, @markj wrote:

This should be documented in mount_nullfs.8. The implementation looks ok to me.

I will after the patch is finalized.

The name sounds a bit strange to me. The mount_nullfs terminology explains what "bypass" means, but it's still a bit unclear IMO. What do you think about unix_private, nounix_private?

For me, 'private' is worse. What exactly is the scope where the socket becomes private? People would think about jails or whatever namespace restriction they intend, but not the pass from upper to lower.
I can rename user-visible option to unixbypass e.g.

unixbypass or unix_bypass is ok with me.

[kib]

Rename the option to 'unixbypass'.
Add documentation.

[markj]

sbin/mount_nullfs/mount_nullfs.8

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(On Diff #163872)

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(On Diff #163872)

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(On Diff #163872)

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(On Diff #163872)

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(On Diff #163872)

sys/fs/nullfs/null.h

42

Rename the flag and VOP vector as well, to keep things consistent?

[kib]

sys/fs/nullfs/null.h

42

Internally the VOPs are called VOP_UNP_something, so I am consistent I think.

[kib]

sys/fs/nullfs/null.h

42

I can change if you insist, but unp is the established name in the kernel sources.