[fuse-devel] Intercepting regular low level mknod operations in FUSE

[maciver <ro...@gm...>]

With lots of support regarding FUSE (Filesystem in Userspace) with high level
operations classified in fuse_operations Struct, together with it is tons of
examples that relates how fuse_operations works.

However, what I am trying to achieve required the use of:

void(*  lookup )(fuse_req_t req, fuse_ino_t parent, const char *name)
void(*  mknod )(fuse_req_t req, fuse_ino_t parent, const char *name, mode_t
mode, dev_t rdev)

in fuse_lowlevel_ops Struct.

I am not trying to the change the function of this two method, but just to
intercept the meta data that passes through and store them in a cache.

>From sample traces, for a new file creation, I see that LOOKUP() is always
called first to identify if a file node exist, if it does, it will be
returned. Else ERROR will be returned and MKNOD() will be called to create
the file node then OPEN() and so on.

So what I am trying to achieve is to have my filesystem maintaining a cache
record. MKNOD will continue to do it normal operation while I'll just
intercept the meta data record and store it in my cache. When LOOKUP is
called for file node lookup, I'll check with my cache to see if it is
available, if it is, I'll return. Else it will go on to check using it
normal operation.

Now the problem is, I couldn't find any documentation regarding the
implementation of low-level MKNOD() where file nodes are created and
LOOKUP() where file nodes are retrieved. So when the function call is passed
from VFS to my mounted filesystem, I am not sure where I should create my
file node to (based on normal filesystem operation). And what are the
conditions to meet.

I will be glad if someone can direct me to the correct direction and
established examples that I can refer to. Thanks.
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