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45 lines
1.8 KiB
C++
45 lines
1.8 KiB
C++
/*
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ISC License
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Copyright (c) 2026, Antonio SJ Musumeci <trapexit@spawn.link>
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Permission to use, copy, modify, and/or distribute this software for any
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purpose with or without fee is hereby granted, provided that the above
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copyright notice and this permission notice appear in all copies.
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THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
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OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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*/
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#pragma once
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#include <cstddef>
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#include <shared_mutex>
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#include <sys/types.h>
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/* A borrowed, descriptor-referenced region of a branch file that a read
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reply can splice into /dev/fuse without the data crossing userspace.
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The filesystem fills it; libfuse never owns or closes the fd.
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The reply splices from fd several times, so the filesystem may park
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a shared lock in lock to keep fd bound to the same file until every
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read from fd is done (staged into the reply). The reply path
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releases it as soon as that staging finishes, whether or not the
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reply is then successfully delivered: fd is not read again either
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way, and once the READ is answered the kernel may send RELEASE, so
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the filesystem may free what the lock lives in. A fallback reached
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instead DURING staging (fd itself declined or ran out of data)
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leaves the lock held; it is released when the region goes out of
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scope, before any fallback read. */
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struct FileRegion
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{
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int fd = -1;
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off_t offset = 0;
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size_t size = 0;
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std::shared_lock<std::shared_mutex> lock;
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};
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