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https://github.com/ceph/ceph
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95 lines
2.1 KiB
ReStructuredText
95 lines
2.1 KiB
ReStructuredText
==============
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Librados (C)
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==============
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.. highlight:: c
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`Librados` provides low-level access to the RADOS service. For an
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overview of RADOS, see :doc:`/architecture`.
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Example: connecting and writing an object
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=========================================
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To use `Librados`, you instantiate a :c:type:`rados_t` variable and
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call :c:func:`rados_create()` with a pointer to it::
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int err;
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rados_t cluster;
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err = rados_create(&cluster, NULL);
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if (err < 0) {
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fprintf(stderr, "%s: cannot open a rados connection: %s\n", argv[0], strerror(-err));
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exit(1);
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}
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Then you open an "IO context", a :c:type:`rados_ioctx_t`, with :c:func:`rados_ioctx_create()`::
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rados_ioctx_t io;
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char *poolname = "mypool";
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err = rados_ioctx_create(cluster, poolname, &io);
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if (err < 0) {
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fprintf(stderr, "%s: cannot open rados pool %s: %s\n", argv[0], poolname, strerror(-err));
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rados_shutdown(conn);
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exit(1);
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}
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Note that the pool you try to access must exist.
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Then you can use the RADOS data manipulation functions, for example
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write into an object called ``greeting`` with
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:c:func:`rados_write_full()`::
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err = rados_write_full(io, "greeting", "hello", 5);
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if (err < 0) {
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fprintf(stderr, "%s: cannot write pool %s: %s\n", argv[0], poolname, strerror(-err));
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rados_ioctx_destroy(io);
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rados_shutdown(conn);
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exit(1);
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}
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In the end, you'll want to close your IO context and connection to RADOS with :c:func:`rados_ioctx_destroy()` and :c:func:`rados_shutdown()`::
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rados_ioctx_destroy(io);
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rados_shutdown(conn);
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API calls
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=========
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.. todo:: this document mentions individual entries, and not all of
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librados.h, because processing the whole file in takes 2
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minutes
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.. .. doxygenfile:: rados/librados.h
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Cluster operations
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------------------
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.. doxygentypedef:: rados_t
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.. doxygenfunction:: rados_create
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.. doxygenfunction:: rados_shutdown
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IO Context
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----------
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.. doxygentypedef:: rados_ioctx_t
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.. doxygenfunction:: rados_ioctx_create
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.. doxygenfunction:: rados_ioctx_destroy
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Operations on objects
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---------------------
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.. doxygenfunction:: rados_write_full
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