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Commit ce69f298 authored by Daniel Rosenberg's avatar Daniel Rosenberg Committed by David Anderson
Browse files

libsnapshot: Don't try to truncate block devices 

When we're writing to a block device, we can't truncate. Ignore those
commands. Truncate mostly just saves time in the read phase by chopping
off unused data in the event finalize wasn't called.

Bug: 172026020
Test: cow_api_test
Change-Id: I3befc71fa9597edf8243d0f9e17440db91409aea
parent 99ed2152

fs_mgr/libsnapshot/cow_writer.cpp

+21 −4
Original line number Diff line number Diff line
@@ -122,6 +122,13 @@ bool CowWriter::SetFd(android::base::borrowed_fd fd) { 
        is_dev_null_ = true;

    } else {

        fd_ = fd;



        struct stat stat;

        if (fstat(fd.get(), &stat) < 0) {

            PLOG(ERROR) << "fstat failed";

            return false;

        }

        is_block_device_ = S_ISBLK(stat.st_mode);

    }

    return true;

}
@@ -217,12 +224,11 @@ bool CowWriter::OpenForAppend(uint64_t label) { 
    // Free reader so we own the descriptor position again.

    reader = nullptr;



    // Position for new writing

    if (ftruncate(fd_.get(), next_op_pos_) != 0) {

        PLOG(ERROR) << "Failed to trim file";

    // Remove excess data

    if (!Truncate(next_op_pos_)) {

        return false;

    }

    if (lseek(fd_.get(), 0, SEEK_END) < 0) {

    if (lseek(fd_.get(), next_op_pos_, SEEK_SET) < 0) {

        PLOG(ERROR) << "lseek failed";

        return false;

    }
@@ -445,5 +451,16 @@ bool CowWriter::CommitMerge(int merged_ops) { 
    return Sync();

}



bool CowWriter::Truncate(off_t length) {

    if (is_dev_null_ || is_block_device_) {

        return true;

    }

    if (ftruncate(fd_.get(), length) < 0) {

        PLOG(ERROR) << "Failed to truncate.";

        return false;

    }

    return true;

}



}  // namespace snapshot

}  // namespace android

fs_mgr/libsnapshot/include/libsnapshot/cow_writer.h

+2 −0
Original line number Diff line number Diff line
@@ -123,6 +123,7 @@ class CowWriter : public ICowWriter { 


    bool SetFd(android::base::borrowed_fd fd);

    bool Sync();

    bool Truncate(off_t length);



  private:

    android::base::unique_fd owned_fd_;
@@ -133,6 +134,7 @@ class CowWriter : public ICowWriter { 
    uint64_t next_op_pos_ = 0;

    bool is_dev_null_ = false;

    bool merge_in_progress_ = false;

    bool is_block_device_ = false;



    // :TODO: this is not efficient, but stringstream ubsan aborts because some

    // bytes overflow a signed char.