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 (struct nbd_handle *h, uint64_t count,
12 uint64_t offset, uint32_t flags);
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15 Issue the cache (prefetch) command to the NBD server, which if
16 supported by the server causes data to be prefetched into faster
17 storage by the server, speeding up a subsequent nbd_pread(3) call. The
18 server can also silently ignore this command. Note this will generally
19 return an error if nbd_can_cache(3) is false.
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21 The "flags" parameter must be 0 for now (it exists for future NBD
22 protocol extensions).
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24 By default, libnbd will reject attempts to use this function with
25 parameters that are likely to result in server failure, such as
26 requesting an unknown command flag. The nbd_set_strict_mode(3)
27 function can be used to alter which scenarios should await a server
28 reply rather than failing fast.
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31 If the call is successful the function returns 0.
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34 On error "-1" is returned.
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36 Refer to "ERROR HANDLING" in libnbd(3) for how to get further details
37 of the error.
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40 The handle must be connected with the server, otherwise this call will
41 return an error.
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44 This function first appeared in libnbd 1.0.
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46 If you need to test if this function is available at compile time check
47 if the following macro is defined:
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49 #define LIBNBD_HAVE_NBD_CACHE 1
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52 nbd_aio_cache(3), nbd_can_cache(3), nbd_create(3), nbd_pread(3),
53 nbd_set_strict_mode(3), libnbd(3).
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56 Eric Blake
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58 Richard W.M. Jones
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61 Copyright (C) 2019-2021 Red Hat Inc.
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64 This library is free software; you can redistribute it and/or modify it
65 under the terms of the GNU Lesser General Public License as published
66 by the Free Software Foundation; either version 2 of the License, or
67 (at your option) any later version.
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69 This library is distributed in the hope that it will be useful, but
70 WITHOUT ANY WARRANTY; without even the implied warranty of
71 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
72 Lesser General Public License for more details.
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74 You should have received a copy of the GNU Lesser General Public
75 License along with this library; if not, write to the Free Software
76 Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
77 02110-1301 USA
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81libnbd-1.7.12 2021-05-29 nbd_cache(3)