[fuse-discuss] Major problems with |fuse_get_context()| and global variables...

[Roland Mainz]

Hi!

----

I did a quick look at the FUSE sources at
http://src.opensolaris.org/source/xref/fuse/ and found the following
piece of code in the public header
http://src.opensolaris.org/source/xref/fuse/libfuse/include/fuse.h
-- snip --
    473 /**
    474  * Get the current context
    475  *
    476  * The context is only valid for the duration of a filesystem
    477  * operation, and thus must not be stored and used later.
    478  *
    479  * @param f the FUSE handle
    480  * @return the context
    481  */
    482 struct fuse_context *fuse_get_context(void);
-- snip --

I would STRONGLY suggest to avoid the usage of such global or
thread-local variables. IMO they cause huge pain and development
problems for multithreaded applications and usually result in the use of
locking and other horrific stunts in more complex applications (I'm
currently in this hell with ksh83/libshell and it's not really fun top
cleanup a large pile of global variables... ;-( ).

My suggestion would be that each callback function called by FUSE
accepts a |struct fuse_context *| as first parameter (and remove
|fuse_get_context()|&co. completely) instead - this would avoid the use
of global data and it's side-effects entirely.

The resulting |fuse_operations| would look like this:
-- snip --
struct fuse_operations {
    int (*getattr) (struct fuse_context *, const char *, struct stat *);

    int (*readlink) (struct fuse_context *, const char *, char *,
size_t);

    int (*getdir) (struct fuse_context *, const char *, fuse_dirh_t,
fuse_dirfil_t);

    int (*mknod) (struct fuse_context *, const char *, mode_t, dev_t);

    int (*mkdir) (struct fuse_context *, const char *, mode_t);

    int (*unlink) (struct fuse_context *, const char *);

    int (*rmdir) (struct fuse_context *, const char *);

    int (*symlink) (struct fuse_context *, const char *, const char *);

    int (*rename) (struct fuse_context *, const char *, const char *);

    int (*link) (struct fuse_context *, const char *, const char *);

    int (*chmod) (struct fuse_context *, const char *, mode_t);

    int (*chown) (struct fuse_context *, const char *, uid_t, gid_t);

    int (*truncate) (struct fuse_context *, const char *, off_t);

    int (*utime) (struct fuse_context *, const char *, struct utimbuf
*);

    int (*open) (struct fuse_context *, const char *, struct
fuse_file_info *);

    int (*read) (struct fuse_context *, const char *, char *, size_t,
off_t, struct fuse_file_info *);

    int (*write) (struct fuse_context *, const char *, const char *,
size_t, off_t,
                  struct fuse_file_info *);

    int (*statfs) (struct fuse_context *, const char *, struct statvfs
*);

    int (*flush) (struct fuse_context *, const char *, struct
fuse_file_info *);

    int (*release) (struct fuse_context *, const char *, struct
fuse_file_info *);

    int (*fsync) (struct fuse_context *, const char *, int, struct
fuse_file_info *);

    int (*setxattr) (struct fuse_context *, const char *, const char *,
const char *, size_t, int);

    int (*getxattr) (struct fuse_context *, const char *, const char *,
char *, size_t);

    int (*listxattr) (struct fuse_context *, const char *, char *,
size_t);

    int (*removexattr) (struct fuse_context *, const char *, const char
*);

    int (*opendir) (struct fuse_context *, const char *, struct
fuse_file_info *);

    int (*readdir) (struct fuse_context *, const char *, void *,
fuse_fill_dir_t, off_t,
                    struct fuse_file_info *);

    int (*releasedir) (struct fuse_context *, const char *, struct
fuse_file_info *);

    int (*fsyncdir) (struct fuse_context *, const char *, int, struct
fuse_file_info *);

    void *(*init) (struct fuse_context *);

    void (*destroy) (struct fuse_context *, void *);

    int (*access) (struct fuse_context *, const char *, int);

    int (*create) (struct fuse_context *, const char *, mode_t, struct
fuse_file_info *);

    int (*ftruncate) (struct fuse_context *, const char *, off_t, struct
fuse_file_info *);

    int (*fgetattr) (struct fuse_context *, const char *, struct stat *,
struct fuse_file_info *);
};
-- snip --

----

Bye,
Roland

-- 
  __ .  . __
 (o.\ \/ /.o) roland.mainz at nrubsig.org
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