From owner-freebsd-fs@freebsd.org  Thu Jul 23 06:41:44 2015
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Date: Thu, 23 Jul 2015 09:41:39 +0300
From: Konstantin Belousov <kostikbel@gmail.com>
To: Simon Brugger <simon.brugger@gmail.com>
Cc: freebsd-fs@freebsd.org
Subject: Re: Need help to understand inodes in FAT implementation
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On Wed, Jul 22, 2015 at 10:46:01PM -0700, Simon Brugger wrote:
> The FAT filesystem is a design from Microsoft and the whole Windows
> universe. As you probably know, FAT does not support Inodes like ext3 or
> other UNIX/LINUX filesystem.
> 
> The FreeBSD kernel provide a FAT filesystem driver but I've problems to
> understand the code and need help for answering the following questions:
> 
>    - Inodes must be generated on the fly by file access. When exactly does
>    this happened?
Inodes are not generated. The inode numbers are. Look at the
sys/fs/msdosfs/msdosfs_vnops.c:msdosfs_getattr() to see how. The struct
vattr va_fileid field is returned from VOP_GETATTR() to userspace as the
struct stat st_ino.

>    - How does FreeBSD generate Inodes?
>    - How does the kernel FAT driver manage the file descriptors?
Kernel FAT driver does not manage file descriptors.