1nbd_cache(3) LIBNBD nbd_cache(3)
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6 nbd_cache - send cache (prefetch) command to the NBD server
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9 #include <libnbd.h>
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11 int nbd_cache (
12 struct nbd_handle *h, uint64_t count,
13 uint64_t offset, uint32_t flags
14 );
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17 Issue the cache (prefetch) command to the NBD server, which if
18 supported by the server causes data to be prefetched into faster
19 storage by the server, speeding up a subsequent nbd_pread(3) call. The
20 server can also silently ignore this command. Note this will generally
21 return an error if nbd_can_cache(3) is false.
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23 Note that not all servers can support a "count" of 4GiB or larger. The
24 NBD protocol does not yet have a way for a client to learn if the
25 server will enforce an even smaller maximum cache size, although a
26 future extension may add a constraint visible in nbd_get_block_size(3).
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28 The "flags" parameter must be 0 for now (it exists for future NBD
29 protocol extensions).
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31 By default, libnbd will reject attempts to use this function with
32 parameters that are likely to result in server failure, such as
33 requesting an unknown command flag. The nbd_set_strict_mode(3)
34 function can be used to alter which scenarios should await a server
35 reply rather than failing fast.
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38 If the call is successful the function returns 0.
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41 On error -1 is returned.
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43 Refer to "ERROR HANDLING" in libnbd(3) for how to get further details
44 of the error.
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46 The following parameters must not be NULL: "h". For more information
47 see "Non-NULL parameters" in libnbd(3).
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50 The handle must be connected with the server, otherwise this call will
51 return an error.
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54 This function first appeared in libnbd 1.0.
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56 If you need to test if this function is available at compile time check
57 if the following macro is defined:
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59 #define LIBNBD_HAVE_NBD_CACHE 1
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62 nbd_aio_cache(3), nbd_can_cache(3), nbd_create(3),
63 nbd_get_block_size(3), nbd_pread(3), nbd_set_strict_mode(3), libnbd(3).
64
66 Eric Blake
67
68 Richard W.M. Jones
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71 Copyright Red Hat
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74 This library is free software; you can redistribute it and/or modify it
75 under the terms of the GNU Lesser General Public License as published
76 by the Free Software Foundation; either version 2 of the License, or
77 (at your option) any later version.
78
79 This library is distributed in the hope that it will be useful, but
80 WITHOUT ANY WARRANTY; without even the implied warranty of
81 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
82 Lesser General Public License for more details.
83
84 You should have received a copy of the GNU Lesser General Public
85 License along with this library; if not, write to the Free Software
86 Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
87 02110-1301 USA
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91libnbd-1.16.5 2023-09-26 nbd_cache(3)