Use internal error codes instead of UNIX errnos

[jdarcy]

Over the years we've had many problems with the meaning of various UNIX errnos being overloaded, usually because some subsystem uses a particular error code internally. An ESTALE generated internally means something different than an ESTALE from a posix syscall. ENOTCONN has too many different meanings even to keep track of. There are also portability issues when a particular errno value doesn't exist or has a different meaning on NetBSD/FreeBSD than on Linux. Using an internal error type instead of overloading random errno values with random meanings will help avoid both problems.

My proposal is to have our own set of error values, and only use those internally. Whenever we need to convert back and forth - e.g. from a syscall/libc errno to an internal gf_errno or in the opposite direction when reporting errors via FUSE/NFS - we can use a conversion table by default, but there might also be many cases where this default needs to be overridden.

[amarts]

Yes, we should have had this long time ago. Now is the good time never the less. I am thinking to have similar approach for #273 too. We need our own stat structure which can capture lot more information and also has option for reserved fields. When passing it to higher layers, we can convert it and send.

[amarts]

libglusterfs/src/compat-errno.h can be used i guess. Btw, this file was used to handle different errno's in different OS to be mapped properly at protocol level. But as we use errno extensively at every xlator level to make decisions, we should be doing this conversion at posix/client-protocol and fuse/nfs/gfapi/server-protocol level. All internal xlators should use our own errno.

[gluster-ant]

A patch https://review.gluster.org/18069 has been posted that references this issue.
Commit message: improvements to errno to error code conversion

[gluster-ant]

A patch https://review.gluster.org/18069 has been posted that references this issue.
Commit message: improvements to errno to error code conversion

[gluster-ant]

A patch https://review.gluster.org/18084 has been posted that references this issue.
Commit message: Convert all the errno to error-codes

[gluster-ant]

A patch https://review.gluster.org/18069 has been posted that references this issue.
Commit message: improvements to errno to error code conversion

[gluster-ant]

A patch https://review.gluster.org/18087 has been posted that references this issue.
Commit message: Convert all the errno to error-codes

[gluster-ant]

A patch https://review.gluster.org/18069 has been posted that references this issue.
Commit message: improvements to errno to error code conversion