Ensure that when a file is extended using FCNTL_SIZE_HINT the last page is allocated on disk, even if the file will only use part of it.

FossilOrigin-Name: c7f84717d61197afa9e0ac607c4b349361e6e2b7

1 files changed, 13 insertions, 10 deletions

diff --git a/src/os_unix.c b/src/os_unix.c
index 8314e4f67..f802d9cd1 100644
--- a/src/os_unix.c
+++ b/src/os_unix.c
@@ -3709,24 +3709,27 @@ static int fcntlSizeHint(unixFile *pFile, i64 nByte){
       }while( err==EINTR );
       if( err ) return SQLITE_IOERR_WRITE;
 #else
-      /* If the OS does not have posix_fallocate(), fake it. First use
-      ** ftruncate() to set the file size, then write a single byte to
-      ** the last byte in each block within the extended region. This
-      ** is the same technique used by glibc to implement posix_fallocate()
-      ** on systems that do not have a real fallocate() system call.
+      /* If the OS does not have posix_fallocate(), fake it. Write a 
+      ** single byte to the last byte in each block that falls entirely
+      ** within the extended region. Then, if required, a single byte
+      ** at offset (nSize-1), to set the size of the file correctly.
+      ** This is a similar technique to that used by glibc on systems
+      ** that do not have a real fallocate() call.
       */
       int nBlk = buf.st_blksize;  /* File-system block size */
       i64 iWrite;                 /* Next offset to write to */
 
       iWrite = ((buf.st_size + 2*nBlk - 1)/nBlk)*nBlk-1;
-      while( iWrite<nSize ){
+      assert( iWrite>=buf.st_size );
+      assert( (iWrite/nBlk)==((buf.st_size+nBlk-1)/nBlk) );
+      assert( ((iWrite+1)%nBlk)==0 );
+      for(/*no-op*/; iWrite<nSize; iWrite+=nBlk ){
         int nWrite = seekAndWrite(pFile, iWrite, "", 1);
         if( nWrite!=1 ) return SQLITE_IOERR_WRITE;
-        iWrite += nBlk;
       }
-      if( robust_ftruncate(pFile->h, nSize) ){
-        pFile->lastErrno = errno;
-        return unixLogError(SQLITE_IOERR_TRUNCATE, "ftruncate", pFile->zPath);
+      if( nSize%nBlk ){
+        int nWrite = seekAndWrite(pFile, nSize-1, "", 1);
+        if( nWrite!=1 ) return SQLITE_IOERR_WRITE;
       }
 #endif
     }