I intentionally corrupted a zpool to induce an I/O error in a file, in this case, /usr/lib/x86_64-linux-gnu/gconv/IBM1390.so# ls -l /usr/lib/x86_64-linux-gnu/gconv/IBM1390.so-rw-r--r-- 1 root root 231,496 2014-03-24 06:26 /usr/lib/x86_64-linux-gnu/gconv/IBM1390.so# cat /usr/lib/x86_64-linux-gnu/gconv/IBM1390.so > /dev/nullcat: /usr/lib/x86_64-linux-gnu/gconv/IBM1390.so: Input/output errorWhen I read the file, Python 3.3.5 and 3.4.0 check for EIO and raise an exception:>>> open("/usr/lib/x86_64-linux-gnu/gconv/IBM1390.so", "rb").read()Traceback (most recent call last):  File "<stdin>", line 1, in <module>OSError: [Errno 5] Input/output errorbut Python 2.7.6 does not:# python2Python 2.7.6 (default, Mar 22 2014, 22:59:56) [GCC 4.8.2] on linux2Type "help", "copyright", "credits" or "license" for more information.>>> x = open("/usr/lib/x86_64-linux-gnu/gconv/IBM1390.so", "rb").read()>>> len(x)131072

Python 2.7 uses C fopen() and fread(), so what happens probably is that fread() silences the error.

> Python 2.7 uses C fopen() and fread(), so what happens probably is that fread() silences the error.I see that file_read() checks ferror() if fread() returned 0. I would nice to run the test in strace and attach the output of strace to see if the EIO is returneded by the kernel at least.

@ivank: Can you please answer to questions? It's hard to understand the issue. Without more information, I would suggest to close the issue.

I'm finding it hard to reproduce the bug again with more zpool corruption.  (I see the `IOError: [Errno 5] Input/output error` exception now.)  I do remember that in the reported case, Python 3.4, node.js, and OpenJDK 7 threw an EIO exception, but Python 2.7 did not.  I tested this multiple times.Right now I can only speculate that Python 2.7 silently stops reading only in certain cases, e.g. depending on how Python's reads are aligned with the first byte that causes EIO.I'm still working on getting it reproduced, please hold off on closing.

2014-04-27 5:26 GMT+02:00 ivank <report@bugs.python.org>:> (I see the `IOError: [Errno 5] Input/output error` exception now.)Can you please run your test in strace to see system calls?

I'm with Antoine, it's likely a glibc bug.We already had a similar issue with fwrite():http://bugs.python.org/issue17976

ivank, if you know some C, perhaps you could write a trivial program that does an fopen() followed by an fread() of 131072 bytes, and see if the fread() errors out.

I managed to reproduce this again, this time by corrupting data on a btrfs filesystem.$ cat read_error_file.py    import osfname = "/usr/bin/Xorg"size = os.stat(fname).st_sizeprint fname, "stat size:", sizef = open(fname, "rb")print "len(f.read()): ", len(f.read())f.close()f = open(fname, "rb")for i in xrange(size):        try:                f.read(1)        except IOError:                print "IOError at byte %d" % i                breakf.close()$ python read_error_file.py /usr/bin/Xorg stat size: 2331776len(f.read()):  716800IOError at byte 716800Note how the first test does not throw an IOError, but the second one does.The strace for the first test is:open("/usr/bin/Xorg", O_RDONLY)         = 3fstat(3, {st_mode=S_IFREG|0755, st_size=2331776, ...}) = 0fstat(3, {st_mode=S_IFREG|0755, st_size=2331776, ...}) = 0lseek(3, 0, SEEK_CUR)                   = 0fstat(3, {st_mode=S_IFREG|0755, st_size=2331776, ...}) = 0mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f1334bd6000lseek(3, 0, SEEK_CUR)                   = 0mmap(NULL, 2334720, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f1332ea6000read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\265M\4\0\0\0\0\0"..., 2330624) = 716800read(3, 0x7f1332f55034, 1613824)        = -1 EIO (Input/output error)mremap(0x7f1332ea6000, 2334720, 720896, MREMAP_MAYMOVE) = 0x7f1332ea6000munmap(0x7f1332ea6000, 720896)          = 0write(1, "len(f.read()):  716800\n", 23len(f.read()):  716800) = 23Note the "-1 EIO (Input/output error)" that gets ignored somewhere.

This problem happens with Python 3.4 as well.$ cat read_error_file.py from __future__ import print_functionimport osfname = "/usr/bin/Xorg"size = os.stat(fname).st_sizeprint(fname, "stat size:", size)f = open(fname, "rb")print("len(f.read()): ", len(f.read()))f.close()f = open(fname, "rb")for i in range(size):        try:                f.read(1)        except IOError:                print("IOError at byte %d" % i)                breakf.close()$ python3 --versionPython 3.4.1$ python3 read_error_file.py/usr/bin/Xorg stat size: 2331776len(f.read()):  716800IOError at byte 716800strace for the first test is:open("/usr/bin/Xorg", O_RDONLY|O_CLOEXEC) = 3fstat(3, {st_mode=S_IFREG|0755, st_size=2331776, ...}) = 0ioctl(3, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, 0x7fff323ac8b0) = -1 ENOTTY (Inappropriate ioctl for device)fstat(3, {st_mode=S_IFREG|0755, st_size=2331776, ...}) = 0lseek(3, 0, SEEK_CUR)                   = 0lseek(3, 0, SEEK_CUR)                   = 0fstat(3, {st_mode=S_IFREG|0755, st_size=2331776, ...}) = 0mmap(NULL, 2334720, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f57884cc000read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\265M\4\0\0\0\0\0"..., 2331777) = 716800read(3, 0x7f578857b030, 1614977)        = -1 EIO (Input/output error)mremap(0x7f57884cc000, 2334720, 720896, MREMAP_MAYMOVE) = 0x7f57884cc000munmap(0x7f57884cc000, 720896)          = 0write(1, "len(f.read()):  716800\n", 23len(f.read()):  716800) = 23close(3)

Here is a patch for FileIO.readall() which should fix the issue. Currently, readall() returns read bytes at the first read() error if a least one call to read() succeed.

LGTM.

New changeset652b62213072 by Victor Stinner in branch '3.4':Issue#21090: io.FileIO.readall() does not ignore I/O errors anymore. Before,http://hg.python.org/cpython/rev/652b62213072New changeset440279cec378 by Victor Stinner in branch 'default':(Merge 3.4) Issue#21090: io.FileIO.readall() does not ignore I/O errorshttp://hg.python.org/cpython/rev/440279cec378

New changeset1492a42b8308 by Victor Stinner in branch '2.7':Issue#21090: io.FileIO.readall() does not ignore I/O errors anymore. Before,http://hg.python.org/cpython/rev/1492a42b8308

For Python 2, file.read() looks wrong: if only checks ferror() if fread() returns 0, whereas Py_UniversalNewlineFread() can call fread() more than once, and according to fread() manual page, fread() result can be different than 0 on error."If an error occurs, or the end of the file is reached, the return value is a short item count (or zero)."http://linux.die.net/man/3/freadAttached fileobject.c rewrites error handling in fileobject.c. The main change if that ferror() is called even if fread() does not return 0.

On IRC, buck1 asked why the following code behaves differently on Python < 3.4 and Python >= 3.4. It is related to this issue in fact.Code:---from __future__ import print_functionfrom os import openptyread, write = openpty()from subprocess import Popenproc = Popen(    ('echo', 'ok'),    stdout=write,    close_fds=True,)from os import fdopenfdopen(write, 'w').close()with fdopen(read) as stdout:    print('STDOUT', stdout.read())print('exit code:', proc.wait())---Simplified example:---import io, osread, write = os.openpty()os.write(write, b'ok\n')os.close(write)with io.FileIO(read, closefd=False) as fp:    print(fp.readall())---On Python < 3.4, it displays "ok", whereas Python 3.4 and later fail with OSError(5, 'Input/output error' on readall().Another example:---import osread, write = os.openpty()os.write(write, b'ok\n')os.close(write)print("read: %r" % os.read(read, 4096))print("read: %r" % os.read(read, 4096))---The first read syscall succeed, even if the write end is already called. But the second read syscall fails with EIO.

The Python 2.7 issue (using fread without checking for interrupts) looks like a duplicate ofhttp://bugs.python.org/issue1633941