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e469285fe3
in the case that the map limit is reached, we'll fall back to reading the file into memory normally.
44 lines
1.3 KiB
Go
44 lines
1.3 KiB
Go
// Package syswrap wraps syscalls (just mmap right now) in order to impose a
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// global in-process limit on the maximum number of active mmaps.
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package syswrap
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import (
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"sync/atomic"
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"syscall"
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"github.com/pkg/errors"
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)
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var mapCount uint64
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var ErrMaxMapCountReached = errors.New("maximum map count reached")
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// MaxMapCount default to slightly less than the typical
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// default on Linux (65K). We want to leave some
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// overhead for (e.g.) the Go runtime.
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var MaxMapCount uint64 = 60000
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// Mmap increments the global map count, and then calls syscall.Mmap. It
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// decrements the map count and returns an error if the count was over the
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// limit. If syscall.Mmap returns an error it also decrements the count.
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func Mmap(fd int, offset int64, length int, prot int, flags int) (data []byte, err error) {
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if newCount := atomic.AddUint64(&mapCount, 1); newCount > MaxMapCount {
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atomic.AddUint64(&mapCount, ^uint64(0)) // decrement
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return nil, ErrMaxMapCountReached
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}
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data, err = syscall.Mmap(fd, offset, length, prot, flags)
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if err != nil {
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atomic.AddUint64(&mapCount, ^uint64(0)) // decrement
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}
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return data, err
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}
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// Munmap calls sycall.Munmap, and then decrements the global map count if there
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// was no error.
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func Munmap(b []byte) (err error) {
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err = syscall.Munmap(b)
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if err == nil {
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atomic.AddUint64(&mapCount, ^uint64(0)) // decrement
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}
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return err
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}
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