add rdrw open disk mode

[ekodian]

Add RDWR mode for diskfs.Open(...), so partitions could be resized without exclusive write access. For example growpart uses sgdisk to resize partitions on running systems.

[deitch]

Isn't that dangerous? When the kernel opens a disk, it almost always opens it exclusive, does it not?

[ekodian]

Yes, but you can do it and for example cloud-int does this thing on start, using growpart to extend disk. I think - how you open disk is solely a user's responsibility.

[deitch]

solely a user's responsibility

Which is the argument I have made over and over again with other projects, and here I am arguing against it. Hoisted on my own petard. Good point!