Solaris: Mounting a file system on an application's handlers_问答_开发者

When mounting an NFS filesystem, all data handling goes through the nfs client. How can I write my own handlers to use something other than NFS?

An alternative would be a localhost NFS server but that seams 开发者_如何学编程awfully inefficient

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Example of what should happen

Normally with a filesystem you get: app reads/writes filesystem, Solaris sees where it is mounted and if it is disk then it reads/writes the disk. If it is software mirror it reads and writes to the mirror software. If it it is NFS it reads and writes to a remote NFS server. I want it to read and write to a custom storage software instead of any of the above mentioned options.

Our storage software is for storing files that applications use, it is geared towards large or frequently replaced chunks of data that are not stored in a database. It also includes certain flexibility specific to our company.

Old/existing applications don't know about our new software. All they know to do is read/write a directory. We could tell Solaris that the directory was hosted on NFS and then the NFS server translates and connects to the storage software. We would prefer to tell Solaris about our new program which Solaris has never heard of and then teach Solaris how to talk to our program.

To me this sounds like you'd have to create a pseudo file system. Solaris uses VFS (Virtual File System), under which you can use different filesystems presented as one uniform structure to userspace. Wheither you mount a UFS or NFS or WHATEVER filesystem, users and applications can use filesystem-agnostic tools to interact with VFS.

That means that what you need to create a pseudo file system; a filesystem that manages to handle the vnode and vfs operations (VFS syscall interface), such as read(), write() etc and tie them, (decide what to do when someone opens a particular file etc), to a database-backend of your choice.

http://developers.sun.com/solaris/articles/solaris_internals_ch14_file_system_framework.pdf

Sounds like a big task...

Regards, jgr

You might want to look at some CIFS servers. Alfresco has JCIFS, which is a CIFS server library in Java. It lets you present resources as files, as if they're on a Windows system. So, that means that programs can "mount" these CIFS servers, and you can publish data from your Database via that mechanism.

I have not used it, but that sounds like what you want to do and perhaps something you may want to look in to.

There's also FUSE which lets you create custom file systems in "user mode" rather than having to hack the kernel. It works on Unix and Mac OS, there may be a Windows version as well. This can, in theory, do anything.

For example, there are instances that let you mount a remote system over SSH using a FUSE system. These tend to be written in C/C++.

NFS isn't about mounting a directory on software but mounting a remote share on a directory. Whether the storage device is remote or not doesn't matter that much, it is still through layers of kernel software. Solaris use VFS to provide the first layer. You should implement the underlying one. That would be quite a difficult task for someone already familiar with VFS. As you obviously are not familiar with writing kernel code, I would be very pessimistic about your project ...

What I would suggest you to do instead would be a simpler and less risky approach. Implement an interposition library that would intercept the application I/O code (open, read, write, close, and the likes or perhaps libc fopen, fwrite, you have to figure out what is the best location to interpose) and call your storage software instead.

Here is a simple example of the process: http://developers.sun.com/solaris/articles/lib_interposers.html