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       add_key - add a key to the kernel's key management facility


       #include <keyutils.h>

       key_serial_t add_key(const char *type, const char *description,
                            const void *payload, size_t plen,
                            key_serial_t keyring);


       add_key()  asks  the  kernel  to create or update a key of the given type and description,
       instantiate it with the payload of length plen, and to attach it to the nominated  keyring
       and to return its serial number.

       The key type may reject the data if it's in the wrong format or in some other way invalid.

       If  the  destination  keyring  already  contains a key that matches the specified type and
       description, then, if the key type supports it, that key will be updated rather than a new
       key  being created; if not, a new key will be created and it will displace the link to the
       extant key from the keyring.

       The destination keyring serial number may be that of a valid keyring to which  the  caller
       has write permission, or it may be a special keyring ID:

              This specifies the caller's thread-specific keyring.

              This specifies the caller's process-specific keyring.

              This specifies the caller's session-specific keyring.

              This specifies the caller's UID-specific keyring.

              This specifies the caller's UID-session keyring.


       There  are  a number of key types available in the core key management code, and these can
       be specified to this function:

       “user” Keys of the user-defined key type may contain a blob of  arbitrary  data,  and  the
              description may be any valid string, though it is preferred that the description be
              prefixed with a string representing the service to which the key is of interest and
              a  colon  (for instance “afs:mykey”).  The payload may be empty or NULL for keys of
              this type.

              Keyrings are special key types that may contain links to sequences of other keys of
              any  type.   If  this  interface  is  used to create a keyring, then a NULL payload
              should be specified, and plen should be zero.


       On success add_key() returns the serial number of the  key  it  created  or  updated.   On
       error, the value -1 will be returned and errno will have been set to an appropriate error.


       ENOKEY The keyring doesn't exist.

              The keyring has expired.

              The keyring has been revoked.

       EINVAL The payload data was invalid.

       ENOMEM Insufficient memory to create a key.

       EDQUOT The key quota for this user would be exceeded by creating this key or linking it to
              the keyring.

       EACCES The keyring wasn't available for modification by the user.


       Although this is a Linux system call, it is not present in libc but can be found rather in
       libkeyutils.  When linking, -lkeyutils should be specified to the linker.


       keyctl(1), keyctl(2), request_key(2), keyctl(3), keyrings(7)


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