seaweedfs/weed/mount/weedfs_file_read.go

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package mount
import (
"context"
"io"
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"github.com/hanwen/go-fuse/v2/fuse"
"github.com/seaweedfs/seaweedfs/weed/glog"
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)
/**
* Read data
*
* Read should send exactly the number of bytes requested except
* on EOF or error, otherwise the rest of the data will be
* substituted with zeroes. An exception to this is when the file
* has been opened in 'direct_io' mode, in which case the return
* value of the read system call will reflect the return value of
* this operation.
*
* fi->fh will contain the value set by the open method, or will
* be undefined if the open method didn't set any value.
*
* Valid replies:
* fuse_reply_buf
* fuse_reply_iov
* fuse_reply_data
* fuse_reply_err
*
* @param req request handle
* @param ino the inode number
* @param size number of bytes to read
* @param off offset to read from
* @param fi file information
*/
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func (wfs *WFS) Read(cancel <-chan struct{}, in *fuse.ReadIn, buff []byte) (fuse.ReadResult, fuse.Status) {
fh := wfs.GetHandle(FileHandleId(in.Fh))
if fh == nil {
return nil, fuse.ENOENT
}
fh.orderedMutex.Acquire(context.Background(), 1)
defer fh.orderedMutex.Release(1)
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offset := int64(in.Offset)
totalRead, err := readDataByFileHandle(buff, fh, offset)
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if err != nil {
glog.Warningf("file handle read %s %d: %v", fh.FullPath(), totalRead, err)
return nil, fuse.EIO
}
return fuse.ReadResultData(buff[:totalRead]), fuse.OK
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}
func readDataByFileHandle(buff []byte, fhIn *FileHandle, offset int64) (int64, error) {
// read data from source file
size := len(buff)
fhIn.lockForRead(offset, size)
defer fhIn.unlockForRead(offset, size)
n, err := fhIn.readFromChunks(buff, offset)
if err == nil || err == io.EOF {
maxStop := fhIn.readFromDirtyPages(buff, offset)
n = max(maxStop-offset, n)
}
if err == io.EOF {
err = nil
}
return n, err
}