This is all preliminary. The question is whether we can cover enough
bases for this to be viable.
Here is a proposed struct file. Make f_data opaque (or more opaque),
add f_object, extend fileops (see next structure), Added f_vopflags
to indicate the presence of a vnode in f_data, allowing extended
filesystem ops (e.g. rename, remove, fchown, etc etc etc).
struct file {
LIST_ENTRY(file) f_list;/* list of active files */
short f_flag; /* see fcntl.h */
short f_type; /* descriptor type */
short f_vopflags; /* extended command set flags */
short f_FILLER2; /* (OLD) references from message queue */
struct ucred *f_cred; /* credentials associated with descriptor */
struct fileops *f_ops; /* FILE OPS */
int f_seqcount; /* (sequential heuristic) */
off_t f_nextoff; /* (sequential heuristic) */
off_t f_offset; /* seek position */
caddr_t f_data; /* opaque data (was vnode or socket) */
vm_object_t f_object; /* VM object if mmapable/cacheable, or NULL */
int f_count; /* reference count */
int f_msgcount; /* reference count from message queue */
(additional elements required to support devices, maybe just
a dev_t reference or something like that. I dunno).
};
Proposed fileops structure (shared): Remove ucred argument (obtain ucred
from struct file), add additional functions. Add cached and uncached
versions for fo_read() ... all users will use fo_read() but this way you
can vector fo_read() to a generic VM Object layer which can then call
fo_readnc() for anything that can't be handled by that layer. Same
with fo_write(). Add additional flags to fo_writenc() to handle
write behind, notification that a write occured in the VM layer
(e.g. required by NFS), and other heuristic features.
Note the lack of any reference to the buffer cache here. The filesystem
is responsible for manipulation of the buffer cache if it wants to use
the buffer cache.
I've left the uio in for the moment since it's the most generic way
of passing a buffer.
struct fileops {
int (*fo_read) (fp, uio, flags, p); /* cachable */
int (*fo_readnc) (fp, uio, flags, p); /* uncached */
int (*fo_write) (fp, uio, flags, p); /* cachable */
int (*fo_writenc) (fp, uio, flags, p); /* uncached */
int (*fo_ioctl) (fp, com, data, p);
int (*fo_poll) (fp, events, p);
int (*fo_kqfilter) (fp, knote);
int (*fo_stat) (fp, stat, p);
int (*fo_close) (fp, p);
int (*fo_mmap) (fp, mmap_args);
int (*fo_dump) ( ? )
... others ...
} *f_ops;
-Matt
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