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Overview
Comment:If the read() system call in unix returns fewer bytes than expected, retry it until it either returns zero or an error.
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Timelines: family | ancestors | retry-short-reads
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SHA1: 72256634773f6cba0aabaa3c953cd5daefd50e67
User & Date: drh 2011-11-01 15:45:28
Context
2011-11-01
15:45
If the read() system call in unix returns fewer bytes than expected, retry it until it either returns zero or an error. Closed-Leaf check-in: 72256634 user: drh tags: retry-short-reads
00:52
Version 3.7.9 check-in: c7c6050e user: drh tags: trunk, release, version-3.7.9
Changes
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Changes to src/os_unix.c.

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** See tickets #2741 and #2681.
**
** To avoid stomping the errno value on a failed read the lastErrno value
** is set before returning.
*/
static int seekAndRead(unixFile *id, sqlite3_int64 offset, void *pBuf, int cnt){
  int got;

#if (!defined(USE_PREAD) && !defined(USE_PREAD64))
  i64 newOffset;
#endif
  TIMER_START;

#if defined(USE_PREAD)
  do{ got = osPread(id->h, pBuf, cnt, offset); }while( got<0 && errno==EINTR );
  SimulateIOError( got = -1 );
#elif defined(USE_PREAD64)
  do{ got = osPread64(id->h, pBuf, cnt, offset); }while( got<0 && errno==EINTR);
  SimulateIOError( got = -1 );
#else
................................................................................
    }else{
      ((unixFile*)id)->lastErrno = 0;			
    }
    return -1;
  }
  do{ got = osRead(id->h, pBuf, cnt); }while( got<0 && errno==EINTR );
#endif






  TIMER_END;
  if( got<0 ){
    ((unixFile*)id)->lastErrno = errno;

  }
  OSTRACE(("READ    %-3d %5d %7lld %llu\n", id->h, got, offset, TIMER_ELAPSED));
  return got;
}

/*
** Read data from a file into a buffer.  Return SQLITE_OK if all
** bytes were read successfully and SQLITE_IOERR if anything goes
** wrong.
*/







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** See tickets #2741 and #2681.
**
** To avoid stomping the errno value on a failed read the lastErrno value
** is set before returning.
*/
static int seekAndRead(unixFile *id, sqlite3_int64 offset, void *pBuf, int cnt){
  int got;
  int total = 0;
#if (!defined(USE_PREAD) && !defined(USE_PREAD64))
  i64 newOffset;
#endif
  TIMER_START;
  while( cnt>0 ){
#if defined(USE_PREAD)
    do{ got = osPread(id->h, pBuf, cnt, offset); }while(got<0 && errno==EINTR);
    SimulateIOError( got = -1 );
#elif defined(USE_PREAD64)
    do{ got = osPread64(id->h, pBuf,cnt,offset); }while(got<0 && errno==EINTR);
    SimulateIOError( got = -1 );
#else
................................................................................
      }else{
        ((unixFile*)id)->lastErrno = 0;			
      }
      return -1;
    }
    do{ got = osRead(id->h, pBuf, cnt); }while( got<0 && errno==EINTR );
#endif
    if( got<=0 ) break;
    total += got;
    cnt -= got;
    offset += got;
    pBuf = (void*)(got + (char*)pBuf);
  }
  TIMER_END;
  if( got<0 ){
    ((unixFile*)id)->lastErrno = errno;
    total = got;
  }
  OSTRACE(("READ    %-3d %5d %7lld %llu\n", id->h,total,offset,TIMER_ELAPSED));
  return total;
}

/*
** Read data from a file into a buffer.  Return SQLITE_OK if all
** bytes were read successfully and SQLITE_IOERR if anything goes
** wrong.
*/