37 lines
1.2 KiB
Go
37 lines
1.2 KiB
Go
package fusefrontend
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// Helper functions for sparse files (files with holes)
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import (
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"github.com/hanwen/go-fuse/fuse"
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"github.com/rfjakob/gocryptfs/internal/tlog"
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)
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// Will a write to plaintext offset "off" create a file hole in the ciphertext?
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func (f *file) createsCiphertextHole(plainSize uint64, off int64) bool {
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// Appending a single byte to the file (equivalent to writing to
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// offset=plainSize) would write to "nextBlock".
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nextBlock := f.contentEnc.PlainOffToBlockNo(plainSize)
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// targetBlock is the block the user wants to write to.
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targetBlock := f.contentEnc.PlainOffToBlockNo(uint64(off))
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// If the write goes past the next block, nextBlock will have
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// to be zero-padded to the block boundary and at least nextBlock+1
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// becomes a file hole in the ciphertext.
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return targetBlock > nextBlock
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}
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// Zero-pad the file of size plainSize to the next block boundary
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func (f *file) zeroPad(plainSize uint64) fuse.Status {
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lastBlockLen := plainSize % f.contentEnc.PlainBS()
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missing := f.contentEnc.PlainBS() - lastBlockLen
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if missing == 0 {
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// Already block-aligned
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return fuse.OK
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}
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pad := make([]byte, missing)
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tlog.Debug.Printf("zeroPad: Writing %d bytes\n", missing)
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_, status := f.doWrite(pad, int64(plainSize))
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return status
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}
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