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Merge pull request #175 from Consensys/156-mmap-cherrypick
feat: Initial Support for Memory Mapped Files
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,99 @@ | ||
| package mmap | ||
|
|
||
| import ( | ||
| "errors" | ||
| "io" | ||
| "runtime/debug" | ||
| "syscall" | ||
|
|
||
| pkgErrors "github.com/pkg/errors" | ||
| "golang.org/x/sys/unix" | ||
| ) | ||
|
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| // BlockDevice represents a mmap block device holding a reference to a file descriptor. | ||
| type BlockDevice struct { | ||
| FileDescriptor int | ||
| Data []byte | ||
| } | ||
|
|
||
| // NewBlockDevice creates a BlockDevice from a file | ||
| // descriptor referring either to a regular file or UNIX device node. To | ||
| // speed up reads, a memory map is used. | ||
| func NewBlockDevice(fileDescriptor, sizeBytes int) (*BlockDevice, error) { | ||
| data, err := unix.Mmap(fileDescriptor, 0, sizeBytes, syscall.PROT_READ, syscall.MAP_SHARED) | ||
| if err != nil { | ||
| return nil, pkgErrors.Wrap(err, "failed to memory map block device") | ||
| } | ||
|
|
||
| return &BlockDevice{ | ||
| FileDescriptor: fileDescriptor, | ||
| Data: data, | ||
| }, nil | ||
| } | ||
|
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| // ReadAt reads through the memory map at a given offset. | ||
| func (bd *BlockDevice) ReadAt(p []byte, off int64) (n int, err error) { | ||
| // Let read actions go through the memory map to prevent system | ||
| // call overhead for commonly requested objects. | ||
| if off < 0 { | ||
| return 0, syscall.EINVAL | ||
| } | ||
|
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||
| if off > int64(len(bd.Data)) { | ||
| return 0, io.EOF | ||
| } | ||
| // Install a page fault handler, so that I/O errors against the | ||
| // memory map (e.g., due to disk failure) don't cause us to | ||
| // crash. | ||
| old := debug.SetPanicOnFault(true) | ||
| defer func() { | ||
| debug.SetPanicOnFault(old) | ||
|
|
||
| if recover() != nil { | ||
| err = errors.New("page fault occurred while reading from memory map") | ||
| } | ||
| }() | ||
|
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| n = copy(p, bd.Data[off:]) | ||
| if n < len(p) { | ||
| err = io.EOF | ||
| } | ||
|
|
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| return | ||
| } | ||
|
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| // WriteAt writes at a given offset. | ||
| func (bd *BlockDevice) WriteAt(p []byte, off int64) (int, error) { | ||
| // Let write actions go through the file descriptor. Doing so | ||
| // yields better performance, as writes through a memory map | ||
| // would trigger a page fault that causes data to be read. | ||
| // | ||
| // The pwrite() system call cannot return a size and error at | ||
| // the same time. If an error occurs after one or more bytes are | ||
| // written, it returns the size without an error (a "short | ||
| // write"). As WriteAt() must return an error in those cases, we | ||
| // must invoke pwrite() repeatedly. | ||
| // | ||
| // TODO: Maybe it makes sense to let unaligned writes that would | ||
| // trigger reads anyway to go through the memory map? | ||
| nTotal := 0 | ||
|
|
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| for len(p) > 0 { | ||
| n, err := unix.Pwrite(bd.FileDescriptor, p, off) | ||
| nTotal += n | ||
|
|
||
| if err != nil { | ||
| return nTotal, err | ||
| } | ||
|
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| p = p[n:] | ||
| off += int64(n) | ||
| } | ||
|
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| return nTotal, nil | ||
| } | ||
|
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| // Sync synchronizes a file's in-core state with storage device. | ||
| func (bd *BlockDevice) Sync() error { | ||
| return unix.Fsync(bd.FileDescriptor) | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,51 @@ | ||
| package mmap | ||
|
|
||
| import ( | ||
| pkgErrors "github.com/pkg/errors" | ||
| "golang.org/x/sys/unix" | ||
| ) | ||
|
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||
| // File represents a memory-mapped file. | ||
| type File struct { | ||
| BlockDevice *BlockDevice | ||
| SectorSizeBytes int | ||
| SectorCount int64 | ||
| } | ||
|
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||
| // NewFile constructs a new instance of File. | ||
| func NewFile(path string, minimumSizeBytes int) (*File, error) { | ||
| fd, err := unix.Open(path, unix.O_CREAT|unix.O_RDWR|unix.O_APPEND, 0666) | ||
| if err != nil { | ||
| return nil, pkgErrors.Wrapf(err, "failed to open file %#v", path) | ||
| } | ||
|
|
||
| // Use the block size returned by fstat() to determine the | ||
| // sector size and the number of sectors needed to store the | ||
| // desired amount of space. | ||
| var stat unix.Stat_t | ||
| if err := unix.Fstat(fd, &stat); err != nil { | ||
| return nil, pkgErrors.Wrapf(err, "failed to obtain size of file %#v", path) | ||
| } | ||
|
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| sectorSizeBytes := int(stat.Blksize) | ||
| sectorCount := int64((uint64(minimumSizeBytes) + uint64(stat.Blksize) - 1) / uint64(stat.Blksize)) | ||
| sizeBytes := int64(sectorSizeBytes) * sectorCount | ||
|
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| if err := unix.Ftruncate(fd, sizeBytes); err != nil { | ||
| return nil, pkgErrors.Wrapf(err, "failed to truncate file %#v to %d bytes", path, sizeBytes) | ||
| } | ||
|
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| bd, err := NewBlockDevice(fd, int(sizeBytes)) | ||
|
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| if err != nil { | ||
| return nil, err | ||
| } else if err := unix.Close(fd); err != nil { | ||
| return nil, err | ||
| } | ||
|
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||
| return &File{ | ||
| BlockDevice: bd, | ||
| SectorSizeBytes: sectorSizeBytes, | ||
| SectorCount: sectorCount, | ||
| }, nil | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -1,4 +1,4 @@ | ||
| package testA | ||
| package test | ||
|
|
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| import ( | ||
| "bufio" | ||
|
|
||
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,75 @@ | ||
| package test | ||
|
|
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| import ( | ||
| "os" | ||
| "path/filepath" | ||
| "runtime/debug" | ||
| "testing" | ||
|
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| "github.com/consensys/go-corset/pkg/mmap" | ||
|
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| "github.com/stretchr/testify/require" | ||
| ) | ||
|
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| func Ignored_TestNewBlockDeviceFromFile(t *testing.T) { | ||
| minSizeBytes := 123456 | ||
| blockDevicePath := filepath.Join(t.TempDir(), "test_blockdevice") | ||
|
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| println(blockDevicePath) | ||
|
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| mmapFile, err := mmap.NewFile(blockDevicePath, minSizeBytes) | ||
| require.NoError(t, err) | ||
|
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| sectorSizeBytes := mmapFile.SectorSizeBytes | ||
| sectorCount := mmapFile.SectorCount | ||
| blockDevice := mmapFile.BlockDevice | ||
| // The sector size should be a power of two, and the number of | ||
| // sectors should be sufficient to hold the required space. | ||
| require.LessOrEqual(t, 512, sectorSizeBytes) | ||
| require.Equal(t, 0, sectorSizeBytes&(sectorSizeBytes-1)) | ||
| require.Equal(t, int64((minSizeBytes+sectorSizeBytes-1)/sectorSizeBytes), sectorCount) | ||
|
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| // The file on disk should have a size that corresponds to the | ||
| // sector size and count. | ||
| fileInfo, err := os.Stat(blockDevicePath) | ||
| require.NoError(t, err) | ||
| require.Equal(t, int64(sectorSizeBytes)*sectorCount, fileInfo.Size()) | ||
|
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| // Test read, write and sync operations. | ||
| n, err := blockDevice.WriteAt([]byte("Hello"), 12345) | ||
| require.Equal(t, 5, n) | ||
| require.NoError(t, err) | ||
|
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| var b [16]byte | ||
| n, err = blockDevice.ReadAt(b[:], 12340) | ||
| require.Equal(t, 16, n) | ||
| require.NoError(t, err) | ||
| require.Equal(t, []byte("\x00\x00\x00\x00\x00Hello\x00\x00\x00\x00\x00\x00"), b[:]) | ||
|
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| require.NoError(t, mmapFile.BlockDevice.Sync()) | ||
|
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| // Truncating the file will cause future read access to the | ||
| // memory map underneath the BlockDevice to raise SIGBUS. This | ||
| // may also occur in case of actual I/O errors. These page | ||
| // faults should be caught properly. | ||
| // | ||
| // To be able to implement this, ReadAt() temporary enables the | ||
| // debug.SetPanicOnFault() option. Test that the original value | ||
| // of this option is restored upon completion. | ||
| require.NoError(t, os.Truncate(blockDevicePath, 0)) | ||
|
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| debug.SetPanicOnFault(false) | ||
|
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| n, err = blockDevice.ReadAt(b[:], 12340) | ||
| require.NoError(t, err) | ||
|
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| require.False(t, debug.SetPanicOnFault(false)) | ||
| require.Equal(t, 0, n) | ||
| debug.SetPanicOnFault(true) | ||
|
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| n, err = blockDevice.ReadAt(b[:], 12340) | ||
|
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| require.True(t, debug.SetPanicOnFault(false)) | ||
| require.Equal(t, 0, n) | ||
| require.Error(t, err, "page fault occurred while reading from memory map") | ||
| } |