Description of problem: I received this report about a problem on a network filesystem in which: > strace of a python app on his systems shows an fstat() after every open(). > It's the python built-in open() that does the fstat(). I believe that the fstat being seen is due to this code in Objects/fileobject.c (line 126 below), which is called by builtin-open (actually by file_init) when the fopen() succeeds: 115 /* On Unix, fopen will succeed for directories. 116 In Python, there should be no file objects referring to 117 directories, so we need a check. */ 118 119 static PyFileObject* 120 dircheck(PyFileObject* f) 121 { 122 #if defined(HAVE_FSTAT) && defined(S_IFDIR) && defined(EISDIR) 123 struct stat buf; 124 if (f->f_fp == NULL) 125 return f; >>>126 if (fstat(fileno(f->f_fp), &buf) == 0 && 127 S_ISDIR(buf.st_mode)) { 128 char *msg = strerror(EISDIR); 129 PyObject *exc = PyObject_CallFunction(PyExc_IOError, "(isO)", 130 EISDIR, msg, f->f_name); 131 PyErr_SetObject(PyExc_IOError, exc); 132 Py_XDECREF(exc); 133 return NULL; 134 } 135 #endif 136 return f; 137 } Given that we control the stack (kernel and glibc), perhaps we can patch things to avoid this extra syscall, with some kind of fopen that fails with EISDIR Version-Release number of selected component (if applicable): python-2.7.3-1
The dircheck() call was added by upstream in response to: http://bugs.python.org/issue487277 Initial commit was: http://hg.python.org/cpython/rev/9ba9d1238804 then removed in: http://hg.python.org/cpython/rev/aaf5ee3b8f93 then fixed in: http://hg.python.org/cpython/rev/acf5ecd806af
This bug appears to have been reported against 'rawhide' during the Fedora 19 development cycle. Changing version to '19'. (As we did not run this process for some time, it could affect also pre-Fedora 19 development cycle bugs. We are very sorry. It will help us with cleanup during Fedora 19 End Of Life. Thank you.) More information and reason for this action is here: https://fedoraproject.org/wiki/BugZappers/HouseKeeping/Fedora19
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So, I'd first like to concentrate on Python 3 regarding this, since I found out it does 6 (!) syscalls on opening a file (2x fstat, 2x ioctl and 2xlseek). I'm currently working on a patch that would bring this number down. I'll keep noting my progress in this bug. Python 2 is not that interesting right now, since we'll be switching Fedora to Python 3 as a default, so Python 3 should get all the work.
(In reply to Bohuslav "Slavek" Kabrda from comment #6) > out it does 6 (!) syscalls on opening a file (2x fstat, 2x ioctl and (That was incorrect, Python 3.4 only does 5 - there's just 1 lseek)
So, my first patch for this finally got accepted, removing one of the fstat calls: http://bugs.python.org/issue21679 http://hg.python.org/cpython/rev/3b5279b5bfd1
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