Implement create_snapshot interface for ImageFile

Xun Chen · Xun Chen · commit 7e81fc1a6212 · 2026-01-26T21:08:03.000+08:00
Signed-off-by: Xun Chen &lt;xunchen@hust.edu.cn&gt;
diff --git a/src/image_file.cpp b/src/image_file.cpp
@@ -334,12 +334,12 @@ LSMT::IFileRO *ImageFile::open_lowers(std::vector<ImageConfigNS::LayerConfig> &l
         return NULL;
 
     photon::join_handle *ths[PARALLEL_LOAD_INDEX];
-    std::vector<IFile *> files;
+    std::vector<IFile *> files; // layer0 ... layerN-1
     files.resize(lowers.size(), nullptr);
     auto n = std::min(PARALLEL_LOAD_INDEX, (int)lowers.size());
     LOG_DEBUG("create ` photon threads to open lowers", n);
 
-    ParallelOpenTask tm(files, lowers.size(), lowers);
+    ParallelOpenTask tm(files, lowers.size(), lowers); // layer0 ... layerN-1
     for (auto i = 0; i < n; ++i) {
         ths[i] =
             photon::thread_enable_join(photon::thread_create11(&do_parallel_open_files, this, tm));
@@ -443,7 +443,7 @@ int ImageFile::init_image_file() {
     ImageConfigNS::UpperConfig upper;
     bool record_no_download = false;
     bool has_error = false;
-    auto lowers = conf.lowers();
+    auto lowers = conf.lowers(); // layer0 ... layerN-1
     auto concurrency = image_service.global_conf.prefetchConfig().concurrency();
 
     if (conf.accelerationLayer() && !conf.recordTracePath().empty()) {
@@ -554,3 +554,51 @@ void ImageFile::set_failed(const Ts &...xs) {
         m_exception = estring().appends(xs...);
     }
 }
+
+int ImageFile::create_snapshot(const char *config_path) {
+    // load new config file to get the snapshot layer path
+    // open new upper layer
+    // restack() current RW layer as snapshot layer
+    if(!m_lower_file || !m_upper_file)
+        LOG_ERROR_RETURN(0, -1, "Lower or upper layer is NULL.");
+
+    ImageConfigNS::ImageConfig new_cfg;
+    LSMT::IFileRW *upper_file = nullptr;
+
+    LOG_INFO("Load new config `.", config_path);
+    if (!new_cfg.ParseJSON(config_path)) {
+        LOG_ERROR_RETURN(0, -1, "Error parse new config json: `.", config_path);
+    }
+
+    auto upper = new_cfg.upper();
+    auto lowers = new_cfg.lowers();
+    if(lowers[lowers.size()-1].file() != conf.upper().data())
+        LOG_ERROR_RETURN(0, -1, "The last lower layer(`) should be the same as old upper layer(`) after restack.", lowers[lowers.size()-1].file(), conf.upper().data());
+    if(upper.index() == conf.upper().index() || upper.data() == conf.upper().data())
+        LOG_ERROR_RETURN(0, -1, "The new upper layer(`, `) should be different from the old upper layer(`, `).", upper.data(), upper.index(), conf.upper().data(), conf.upper().index());
+
+    upper_file = open_upper(upper);
+    if (!upper_file)
+        LOG_ERROR_RETURN(0, -1, "Open upper layer failed.");
+    
+    if(((LSMT::IFileRW *)m_file)->restack(upper_file) != 0)
+        LOG_ERRNO_RETURN(0, -1, "Restack new rwlayer failed.");
+    
+    if(m_upper_file) {
+        // transfer the sealed layer from m_upper_file to m_lower_file before m_upper_file is destructed
+        auto sealed = ((LSMT::IFileRW *)m_upper_file)->get_file(0);
+        ((LSMT::IFileRO *)m_lower_file)->insert_file(sealed);
+        ((LSMT::IFileRW *)m_upper_file)->clear_files();
+        delete m_upper_file;
+    }
+    // set m_lower_file->m_index = m_file->m_index->m_backing_index because m_file is not responsible for the destruction of m_backing_index
+    auto combo_index = (LSMT::IComboIndex *)((LSMT::IFileRW *)m_file)->index(); // m_file->m_index
+    ((LSMT::IFileRO *)m_lower_file)->index(combo_index->backing_index());
+    // set m_file->m_index->m_index0 = upper_file->m_index
+    auto upper_file_index = (LSMT::IMemoryIndex0 *)((LSMT::IFileRW *)upper_file)->index(); // upper_file->m_index
+    combo_index->front_index(upper_file_index);
+
+    m_upper_file = upper_file;
+    
+    return 0;
+}
diff --git a/src/image_file.h b/src/image_file.h
@@ -82,6 +82,16 @@ class ImageFile : public photon::fs::ForwardFile {
         return ret;
     }
 
+    ssize_t pwrite(const void *buf, size_t count, off_t offset) override
+    {
+        return m_file->pwrite(buf, count, offset);
+    }
+    
+    ssize_t pread(void *buf, size_t count, off_t offset) override
+    {
+        return m_file->pread(buf, count, offset);
+    }
+        
     ssize_t pwritev(const struct iovec *iov, int iovcnt, off_t offset) override {
         if (read_only) {
             LOG_ERROR_RETURN(EROFS, -1, "writing read only file");
@@ -119,13 +129,7 @@ class ImageFile : public photon::fs::ForwardFile {
 
     int compact(IFile *as);
 
-    int create_snapshot(const char *config_path) {
-        // load new config file to get the snapshot layer path
-        // open new upper layer
-        // restack() current RW layer as snapshot layer
-        LOG_INFO("call create_snapshot, dev_id: `", m_dev_id);
-        return 0;
-    }
+    int create_snapshot(const char *config_path);
 
 private:
     Prefetcher *m_prefetcher = nullptr;
diff --git a/src/overlaybd/lsmt/file.cpp b/src/overlaybd/lsmt/file.cpp
@@ -500,6 +500,20 @@ class LSMTReadOnlyFile : public IFileRW {
         return (IMemoryIndex0 *)m_index;
     }
 
+    virtual int index(const IMemoryIndex *index) override {
+        if(!index || !index->buffer()) {
+            errno = EINVAL;
+            LOG_ERROR("Invalid index!");
+            return -1;
+        }
+        if (m_index != nullptr) {
+            delete m_index;
+            m_index = nullptr;
+        }
+        m_index = (IMemoryIndex *)index;
+        return 0;
+    }
+
     virtual int close() override {
         safe_delete(m_index);
         if (m_file_ownership) {
@@ -523,6 +537,23 @@ class LSMTReadOnlyFile : public IFileRW {
         return m_files;
     }
 
+    virtual IFile *get_file(size_t file_idx) const override {
+        if (file_idx >= m_files.size()) {
+            LOG_ERROR_RETURN(0, nullptr, "file_idx out of range.");
+        }
+        return m_files[file_idx];
+    }
+
+    virtual int insert_file(IFile * file) override {
+        m_files.insert(m_files.begin(), file);
+        return 0;
+    }
+
+    virtual int clear_files() override {
+        m_files.clear();
+        return 0;
+    }
+
     template <typename T1, typename T2, typename T3>
     inline void forward(void *&buffer, T1 &offset, T2 &count, T3 step) {
         (char *&)buffer += step * ALIGNMENT;
@@ -1038,6 +1069,9 @@ class LSMTFile : public LSMTReadOnlyFile {
         m_findex = u->m_findex;
         m_vsize = u->m_vsize;
         ((IComboIndex *)m_index)->commit_index0();
+
+        delete fseal;
+        delete gc_layer;
         return 0;
     }
 
@@ -1333,7 +1367,7 @@ static SegmentMapping *do_load_index(IFile *file, HeaderTrailer *pheader_trailer
     auto ret = file->fstat(&stat);
     if (ret < 0)
         LOG_ERRNO_RETURN(0, nullptr, "failed to stat file.");
-    assert(pht->is_sparse_rw() == false);
+    assert(trailer || pht->is_sparse_rw() == false);
     uint64_t index_bytes;
     if (trailer) {
         if (!pht->is_data_file())
@@ -1738,7 +1772,7 @@ static IMemoryIndex *load_merge_index(vector<IFile *> &files, vector<UUID> &uuid
         }
     }
 
-    std::reverse(files.begin(), files.end());
+    std::reverse(files.begin(), files.end()); // reverse files: layerN-1 ... layer0
     std::reverse(tm.indexes.begin(), tm.indexes.end());
     std::reverse(uuid.begin(), uuid.end());
     auto pmi = merge_memory_indexes((const IMemoryIndex **)&tm.indexes[0], tm.indexes.size());
diff --git a/src/overlaybd/lsmt/file.h b/src/overlaybd/lsmt/file.h
@@ -46,11 +46,19 @@ class IFileRO : public photon::fs::VirtualReadOnlyFile {
 
     virtual IMemoryIndex *index() const = 0;
 
+    virtual int index(const IMemoryIndex *index) = 0;
+
     // return uuid of  m_files[layer_idx];
     virtual int get_uuid(UUID &out, size_t layer_idx = 0) const = 0;
 
     virtual std::vector<IFile *> get_lower_files() const = 0;
 
+    virtual IFile *get_file(size_t file_idx) const = 0;
+
+    virtual int insert_file(IFile * file) = 0;
+
+    virtual int clear_files() = 0;
+
     virtual ssize_t seek_data(off_t begin, off_t end, std::vector<Segment> &segs) = 0;
 
     virtual int flatten(IFile *as) = 0;
diff --git a/src/overlaybd/lsmt/index.cpp b/src/overlaybd/lsmt/index.cpp
@@ -617,6 +617,7 @@ class Index0 : public IComboIndex {
     virtual const IMemoryIndex0 *front_index() const override {
         return this;
     }
+    UNIMPLEMENTED(int front_index(const IMemoryIndex0 *fi) override);
     UNIMPLEMENTED(size_t vsize() const override);
     UNIMPLEMENTED(int commit_index0() override);
 };
@@ -649,6 +650,19 @@ class ComboIndex : public Index0 {
         }
     }
 
+    virtual int front_index(const IMemoryIndex0 *fi) override {
+        if (!fi) {
+            errno = EINVAL;
+            LOG_ERROR("Invalid index!");
+            return -1;
+        }
+        if (m_ownership && m_index0 != nullptr) { // !!!
+            delete m_index0;
+            m_index0 = nullptr;
+        }
+        m_index0 = (Index0 *)fi;
+        return 0;
+    }
     virtual const IMemoryIndex0 *front_index() const override {
         return this->m_index0;
     }
@@ -759,7 +773,8 @@ class ComboIndex : public Index0 {
             p.tag = 0;
             merged_index->insert(p);
         }
-        delete m_backing_index;
+        if(m_ownership) // !!!
+            delete m_backing_index;
         m_backing_index = (Index*)(merged_index->make_read_only_index()); // set ownership=false
         delete merged_index;
         LOG_INFO("rebuild backing index done. {count: `}", m_backing_index->size());
diff --git a/src/overlaybd/lsmt/index.h b/src/overlaybd/lsmt/index.h
@@ -149,6 +149,7 @@ class IComboIndex : public IMemoryIndex0 {
     // backing index must NOT be IMemoryIndex0!
     virtual int backing_index(const IMemoryIndex *bi) = 0;
     virtual const IMemoryIndex *backing_index() const = 0;
+    virtual int front_index(const IMemoryIndex0 *fi) = 0;
     virtual const IMemoryIndex0 *front_index() const = 0;
 
     // dump index0 which needs to compact
diff --git a/src/test/image_service_test.cpp b/src/test/image_service_test.cpp
