From 55cb8920d540139523b30d3781b64dca9bf1e4cd Mon Sep 17 00:00:00 2001
From: Takeshi Nakatani <ggtakec@gmail.com>
Date: Sun, 16 Aug 2020 12:37:11 +0000
Subject: [PATCH] Dynamically determine whether lseek extended options are
 supported

---
 src/fdcache.cpp     | 57 +++++++++++++++++++++++++++++++++++++++++++++
 src/fdcache.h       |  3 +++
 src/sighandlers.cpp |  5 ++++
 3 files changed, 65 insertions(+)

diff --git a/src/fdcache.cpp b/src/fdcache.cpp
index e08ac2b..3fa153e 100644
--- a/src/fdcache.cpp
+++ b/src/fdcache.cpp
@@ -55,6 +55,19 @@ using namespace std;
 static const int MAX_MULTIPART_CNT         = 10 * 1000; // S3 multipart max count
 static const int CHECK_CACHEFILE_PART_SIZE = 1024 * 16;	// Buffer size in PageList::CheckZeroAreaInFile()
 
+//
+// [NOTE]
+// If the following symbols in lseek whence are undefined, define them.
+// If it is not supported by lseek, s3fs judges by the processing result of lseek.
+//
+#ifndef SEEK_DATA
+#define SEEK_DATA               3
+#endif
+#ifndef SEEK_HOLE
+#define SEEK_HOLE               4
+#endif
+#define TMPFILE_FOR_CHECK_HOLE  "/tmp/.s3fs_hole_check.tmp"
+
 //
 // For cache directory top path
 //
@@ -2719,6 +2732,8 @@ string          FdManager::cache_dir;
 bool            FdManager::check_cache_dir_exist(false);
 off_t           FdManager::free_disk_space = 0;
 std::string     FdManager::check_cache_output;
+bool            FdManager::checked_lseek(false);
+bool            FdManager::have_lseek_hole(false);
 
 //------------------------------------------------
 // FdManager class methods
@@ -2928,6 +2943,43 @@ bool FdManager::IsSafeDiskSpace(const char* path, off_t size)
   return size + FdManager::GetEnsureFreeDiskSpace() <= fsize;
 }
 
+bool FdManager::HaveLseekHole(void)
+{
+  if(FdManager::checked_lseek){
+    return FdManager::have_lseek_hole;
+  }
+
+  // create tempolary file
+  int fd;
+  if(-1 == (fd = open(TMPFILE_FOR_CHECK_HOLE, O_CREAT|O_RDWR, 0600))){
+    S3FS_PRN_ERR("failed to open tempolary file(%s) - errno(%d)", TMPFILE_FOR_CHECK_HOLE, errno);
+    FdManager::checked_lseek   = true;
+    FdManager::have_lseek_hole = false;
+    return FdManager::have_lseek_hole;
+  }
+
+  // check SEEK_DATA/SEEK_HOLE options
+  bool result = true;
+  if(-1 == lseek(fd, 0, SEEK_DATA)){
+    if(EINVAL == errno){
+      S3FS_PRN_ERR("lseek does not support SEEK_DATA");
+      result = false;
+    }
+  }
+  if(result && -1 == lseek(fd, 0, SEEK_HOLE)){
+    if(EINVAL == errno){
+      S3FS_PRN_ERR("lseek does not support SEEK_HOLE");
+      result = false;
+    }
+  }
+  close(fd);
+  unlink(TMPFILE_FOR_CHECK_HOLE);
+
+  FdManager::checked_lseek   = true;
+  FdManager::have_lseek_hole = result;
+  return FdManager::have_lseek_hole;
+}
+
 //------------------------------------------------
 // FdManager methods
 //------------------------------------------------
@@ -3470,6 +3522,11 @@ bool FdManager::RawCheckAllCache(FILE* fp, const char* cache_stat_top_dir, const
 
 bool FdManager::CheckAllCache()
 {
+  if(!FdManager::HaveLseekHole()){
+    S3FS_PRN_ERR("lseek does not support SEEK_DATA/SEEK_HOLE, then could not check cache.");
+    return false;
+  }
+
   FILE* fp;
   if(FdManager::check_cache_output.empty()){
     fp = stdout;
diff --git a/src/fdcache.h b/src/fdcache.h
index ffd4c73..f77bc3e 100644
--- a/src/fdcache.h
+++ b/src/fdcache.h
@@ -232,6 +232,8 @@ class FdManager
     static bool            check_cache_dir_exist;
     static off_t           free_disk_space; // limit free disk space
     static std::string     check_cache_output;
+    static bool            checked_lseek;
+    static bool            have_lseek_hole;
 
     fdent_map_t            fent;
 
@@ -265,6 +267,7 @@ class FdManager
     static bool IsSafeDiskSpace(const char* path, off_t size);
     static void FreeReservedDiskSpace(off_t size);
     static bool ReserveDiskSpace(off_t size);
+    static bool HaveLseekHole(void);
 
     // Return FdEntity associated with path, returning NULL on error.  This operation increments the reference count; callers must decrement via Close after use.
     FdEntity* GetFdEntity(const char* path, int existfd = -1);
diff --git a/src/sighandlers.cpp b/src/sighandlers.cpp
index a1edc82..3529757 100644
--- a/src/sighandlers.cpp
+++ b/src/sighandlers.cpp
@@ -93,6 +93,11 @@ void S3fsSignals::HandlerUSR1(int sig)
 
 bool S3fsSignals::SetUsr1Handler(const char* path)
 {
+  if(!FdManager::HaveLseekHole()){
+    S3FS_PRN_ERR("Could not set SIGUSR1 for checking cache, because this system does not support SEEK_DATA/SEEK_HOLE in lseek function.");
+    return false;
+  }
+
   // set output file
   if(!FdManager::SetCacheCheckOutput(path)){
     S3FS_PRN_ERR("Could not set output file(%s) for checking cache.", path ? path : "null(stdout)");