# udev_device_new_from_syspath

## NAME



           udev_device_new_from_syspath, udev_device_new_from_devnum,
           udev_device_new_from_subsystem_sysname,
           udev_device_new_from_device_id, udev_device_new_from_environment,
           udev_device_ref, udev_device_unref - Create, acquire and release a
           udev device object
    


## SYNOPSIS



           **#include <libudev.h>**
    
           **struct udev_device**
                                                            ***udev_device_new_from_syspath(struct udev ***_udev_**,**
                                                            **const char ***_syspath_**);**
    
           **struct udev_device *udev_device_new_from_devnum(struct udev ***_udev_**,**
                                                           **char** _type_**,**
                                                           **dev_t** _devnum_**);**
    
           **struct udev_device**
                                                                      ***udev_device_new_from_subsystem_sysname(struct udev ***_udev_**,**
                                                                      **const char ***_subsystem_**,**
                                                                      **const char ***_sysname_**);**
    
           **struct udev_device**
                                                              ***udev_device_new_from_device_id(struct udev ***_udev_**,**
                                                              **const char ***_id_**);**
    
           **struct udev_device**
                                                                ***udev_device_new_from_environment(struct udev ***_udev_**);**
    
           **struct udev_device**
                                               ***udev_device_ref(struct udev_device ***_udev_device_**);**
    
           **struct udev_device**
                                                 ***udev_device_unref(struct udev_device ***_udev_device_**);**
    


## DESCRIPTION



           **udev_device_new_from_syspath()** , **udev_device_new_from_devnum()** ,
           **udev_device_new_from_subsystem_sysname()** ,
           **udev_device_new_from_device_id()** , and
           **udev_device_new_from_environment()** allocate a new udev device
           object and returns a pointer to it. This object is opaque and must
           not be accessed by the caller via different means than functions
           provided by libudev. Initially, the reference count of the device
           is 1. You can acquire further references, and drop gained
           references via **udev_device_ref()** and **udev_device_unref()**. Once the
           reference count hits 0, the device object is destroyed and freed.
    
           **udev_device_new_from_syspath()** , **udev_device_new_from_devnum()** ,
           **udev_device_new_from_subsystem_sysname()** , and
           **udev_device_new_from_device_id()** create the device object based on
           information found in /sys/, annotated with properties from the
           udev-internal device database. A syspath is any subdirectory of
           /sys/, with the restriction that a subdirectory of /sys/devices
           (or a symlink to one) represents a real device and as such must
           contain a uevent file.  **udev_device_new_from_devnum()** takes a
           device type, which can be **b** for block devices or **c** for character
           devices, as well as a devnum (see makedev(3)).
           **udev_device_new_from_subsystem_sysname()** looks up devices based on
           the provided subsystem and sysname (see
           udev_device_get_subsystem(3) and udev_device_get_sysname(3)) and
           **udev_device_new_from_device_id()** looks up devices based on the
           provided device ID, which is a special string in one of the
           following four forms:
    
           **Table 1. Device ID strings**
           ┌───────────────┬──────────────────────────┐
           │ **Example** │ **Explanation** │
           ├───────────────┼──────────────────────────┤
           │ _b8:2_          │ block device major:minor │
           ├───────────────┼──────────────────────────┤
           │ _c128:1_        │ char device major:minor  │
           ├───────────────┼──────────────────────────┤
           │ _n3_            │ network device ifindex   │
           ├───────────────┼──────────────────────────┤
           │ _+sound:card29_ │ kernel driver core       │
           │               │ subsystem:device name    │
           └───────────────┴──────────────────────────┘
    
           **udev_device_new_from_environment()** creates a device from the
           current environment (see environ(7)). Each key-value pair is
           interpreted in the same way as if it was received in an uevent
           (see udev_monitor_receive_device(3)). The keys **DEVPATH** , **SUBSYSTEM** ,
           **ACTION** , and **SEQNUM** are mandatory.
    


## RETURN VALUE



           On success, **udev_device_new_from_syspath()** ,
           **udev_device_new_from_devnum()** ,
           **udev_device_new_from_subsystem_sysname()** ,
           **udev_device_new_from_device_id()** and
           **udev_device_new_from_environment()** return a pointer to the
           allocated udev device. On failure, **NULL** is returned, and _errno_ is
           set appropriately.  **udev_device_ref()** returns the argument that it
           was passed, unmodified.  **udev_device_unref()** always returns **NULL**.
    


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