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VOP_ACCESS (9)
  • >> VOP_ACCESS (9) ( FreeBSD man: Ядро )

  • BSD mandoc
     

    NAME

    VOP_ACCESS
    
     - check access permissions of a file or Unix domain socket
    
     
    

    SYNOPSIS

       #include <sys/param.h>
       #include <sys/vnode.h>
    int VOP_ACCESS (struct vnode *vp int mode struct ucred *cred struct thread *td);
     

    DESCRIPTION

    This entry point checks the access permissions of the file against the given credentials.

    Its arguments are:

    Fa vp
    The vnode of the file to check.
    Fa mode
    The type of access required.
    Fa cred
    The user credentials to check.
    Fa td
    The thread which is checking.

    The Fa mode is a mask which can contain VREAD VWRITE or VEXEC  

    LOCKS

    The vnode will be locked on entry and should remain locked on return.  

    RETURN VALUES

    If the file is accessible in the specified way, then zero is returned, otherwise an appropriate error code is returned.  

    PSEUDOCODE

    int
    vop_access(struct vnode *vp, int mode, struct ucred *cred, struct thread *td)
    {
        int error;
    
        /*
         * Disallow write attempts on read-only file systems;
         * unless the file is a socket, fifo, or a block or
         * character device resident on the filesystem.
         */
        if (mode & VWRITE) {
            switch (vp->v_type) {
            case VDIR:
            case VLNK:
            case VREG:
                if (vp->v_mount->mnt_flag & MNT_RDONLY)
                    return EROFS;
    
                break;
            }
        }
    
        /* If immutable bit set, nobody gets to write it. */
        if ((mode & VWRITE) && vp has immutable bit set)
            return EPERM;
    
        /* Otherwise, user id 0 always gets access. */
        if (cred->cr_uid == 0)
            return 0;
    
        mask = 0;
    
        /* Otherwise, check the owner. */
        if (cred->cr_uid == owner of vp) {
            if (mode & VEXEC)
                mask |= S_IXUSR;
            if (mode & VREAD)
                mask |= S_IRUSR;
            if (mode & VWRITE)
                mask |= S_IWUSR;
            return (((mode of vp) & mask) == mask ? 0 : EACCES);
        }
    
        /* Otherwise, check the groups. */
        for (i = 0, gp = cred->cr_groups; i < cred->cr_ngroups; i++, gp++)
            if (group of vp == *gp) {
                if (mode & VEXEC)
                    mask |= S_IXGRP;
                if (mode & VREAD)
                    mask |= S_IRGRP;
                if (mode & VWRITE)
                    mask |= S_IWGRP;
                return (((mode of vp) & mask) == mask ? 0 : EACCES);
            }
    
        /* Otherwise, check everyone else. */
        if (mode & VEXEC)
            mask |= S_IXOTH;
        if (mode & VREAD)
            mask |= S_IROTH;
        if (mode & VWRITE)
            mask |= S_IWOTH;
        return (((mode of vp) & mask) == mask ? 0 : EACCES);
    }
    
     

    ERRORS

    Bq Er EPERM
    An attempt was made to change an immutable file.
    Bq Er EACCES
    The permission bits the file mode or the ACL do not permit the requested access.

     

    SEE ALSO

    vaccess(9), vaccess_acl_posix1e9, vnode(9)  

    AUTHORS

    This manual page was written by An Doug Rabson .


     

    Index

    NAME
    SYNOPSIS
    DESCRIPTION
    LOCKS
    RETURN VALUES
    PSEUDOCODE
    ERRORS
    SEE ALSO
    AUTHORS


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