keyctl_read_alloc(3)

1KEYCTL_READ(3)            Linux Key Management Calls            KEYCTL_READ(3)
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NAME

6       keyctl_read - read a key
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SYNOPSIS

9       #include <keyutils.h>
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11       long keyctl_read(key_serial_t key, char *buffer,
12       size_tbuflen);
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14       long keyctl_read_alloc(key_serial_t key, void **_buffer);
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DESCRIPTION

17       keyctl_read() reads the payload of a key if the key type supports it.
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19       The caller must have read permission on a key to be able to read it.
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21       buffer  and  buflen specify the buffer into which the payload data will
22       be placed.  If the buffer is too small, then the full size of the  pay‐
23       load  will be returned, and the contents of the buffer may be overwrit‐
24       ten in some undefined way.
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26       keyctl_read_alloc() is similar to keyctl_read() except  that  it  allo‐
27       cates  a buffer big enough to hold the payload data and places the data
28       in it.  If successful, a pointer to the buffer is placed  in  *_buffer.
29       The caller must free the buffer.
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31       keyctl_read_alloc()  adds  a NUL character after the data it retrieves,
32       though this is not counted in the size value it returns.
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READING KEYRINGS

35       This call can be used to list the contents of a keyring.  The  data  is
36       presented to the user as an array of key_serial_t values, each of which
37       corresponds to a key to which the keyring holds a link.
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39       The size of the keyring will be sizeof(key_serial_t) multiplied by  the
40       number of keys.  The size of key_serial_t is invariant across different
41       word sizes, though the byte-ordering is as appropriate for the kernel.
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RETURN VALUE

44       On success keyctl_read() returns the amount of  data  placed  into  the
45       buffer.   If the buffer was too small, then the size of buffer required
46       will be returned, and the contents of the buffer may  have  been  over‐
47       written in some undefined way.
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49       On  success  keyctl_read_alloc() returns the amount of data in the buf‐
50       fer.
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52       On error, both functions set errno to an appropriate  code  and  return
53       the value -1.
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ERRORS

56       ENOKEY The key specified is invalid.
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58       EKEYEXPIRED
59              The key specified has expired.
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61       EKEYREVOKED
62              The key specified had been revoked.
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64       EACCES The key exists, but is not readable by the calling process.
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66       EOPNOTSUPP
67              The key type does not support reading of the payload data.
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LINKING

70       This  is  a  library  function  that can be found in libkeyutils.  When
71       linking, -lkeyutils should be specified to the linker.
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