[java] "bad file descriptor" is thrown for simple RandomAccessFile.write/seek(0)/read sequence over CharybdeFS partition

[cheremin]

I'm using CharybdeFS to test java applications, and one simple test shows strange behavior.

Steps:

• mount, say, mounted folder with Charybde to, say, data folder. (Both folders must be empty)
• on the top of mounted partition run following java code:

import java.io.*;

public class BadFileDescriptor {
	public static void main( String[] args ) throws IOException {
		final File charybdeDirectory = new File( "mounted" );            
		final File testFile = new File( charybdeDirectory, "test" ); // i.e. 'mounted/test'
		final long writtenValue = 0x1234_5678_9ABC_DEF1L;     //any non trivial value
		try (final RandomAccessFile raf = new RandomAccessFile( testFile, "rw" )) {
			raf.writeLong( writtenValue );
			raf.seek( 0 );
			final long readValue = raf.readLong();                          //<< here is IOException is thrown
			if( readValue != writtenValue ) {
				throw new AssertionError( "Value read (" + readValue + ") is not same as just written (" + writtenValue + ")" );
			}
		}
	}
}

• I'd expect (readValue == writtenValue), and indeed, I've got them equal while running test over "normal" FS folder
• But running over CharybdeFS partition I've got IOException("bad file descriptor") inside .readLong() method call

$JAVA_HOME/bin/java -cp target/classes/ BadFileDescriptor mounted
Exception in thread "main" java.io.IOException: Bad file descriptor
	at java.io.RandomAccessFile.read0(Native Method)
	at java.io.RandomAccessFile.read(RandomAccessFile.java:337)
	at java.io.RandomAccessFile.readInt(RandomAccessFile.java:798)
	at java.io.RandomAccessFile.readLong(RandomAccessFile.java:836)

BTW, java code essentially does just this:

• write 8 bytes to mounted/test
• rewinds file pointer to 0
• tries to read back 8 bytes just written.
• ...and fails with this strange "bad file descriptor" error

So far I was able to reproduce it with java only. (Unfortunately I use python only occasionally, so don't sure how to translate java.io.RandomAccessFile)

Few notes on reproduction:

• test file must be new one. If there is mounted/test already exist in charybde folder -- no exception is thrown.
• java version is 1.8.*
• I was able to reproduce it on 2 systems with different Linux versions

I've tried to run the app under strace, and here is relevant sequence of syscalls:

2201  open("mounted/test", O_RDWR|O_CREAT, 0666) = 14
2201  fstat(14, {st_mode=S_IFREG|0664, st_size=0, ...}) = 0
2201  write(14, "\22", 1)               = 1
2201  write(14, "4", 1)                 = 1
2201  write(14, "V", 1)                 = 1
2201  write(14, "x", 1)                 = 1
2201  write(14, "\232", 1)              = 1
2201  write(14, "\274", 1)              = 1
2201  write(14, "\336", 1)              = 1
2201  write(14, "\361", 1)              = 1
2201  lseek(14, 0, SEEK_SET)            = 0
2201  read(14, 0x7fd7492f5797, 1)       = -1 EBADF (Bad file descriptor)

I omit everything before/after, but nothing in between: here are all syscalls between file open and error.

[bentsi]

confirming this in Python 2.7:

>>> f = open("/tmp/charibdushka/tst", "wr+")
>>> import binascii
>>> hs="123456789ABCDEF1"
>>> hb=binascii.a2b_hex(hs)
>>> f.write(hb)
>>> f.seek(0)
>>> f.read()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IOError: [Errno 9] Bad file descriptor

[bentsi]

More precise code to reproduce the issue:

f = os.open("/mounted_dir",  os.O_RDWR|os.O_CREAT, 0666)
hs="123456789ABCDEF1"
hb=binascii.a2b_hex(hs)
os.write(f, hb)
print ("%s" % os.fstat(f))
os.read(f, 100)

First run (fails with bad file descriptor)

LOOKUP /bentsi
getattr /bentsi
   unique: 64, error: -2 (No such file or directory), outsize: 16
unique: 65, opcode: CREATE (35), nodeid: 1, insize: 63, pid: 24865
create flags: 0x8042 /bentsi 0100644 umask=0022
   create[7] flags: 0x8042 /bentsi
fgetattr[7] /bentsi
   NODEID: 4
   unique: 65, success, outsize: 160
unique: 66, opcode: GETXATTR (22), nodeid: 4, insize: 68, pid: 24865
getxattr /bentsi security.capability 0
   unique: 66, error: -61 (No data available), outsize: 16
unique: 67, opcode: WRITE (16), nodeid: 4, insize: 88, pid: 24865
write[7] 8 bytes to 0 flags: 0x8002
   write[7] 8 bytes to 0
   unique: 67, success, outsize: 24
unique: 68, opcode: GETATTR (3), nodeid: 4, insize: 56, pid: 24865
fgetattr[7] /bentsi
   unique: 68, success, outsize: 120
unique: 69, opcode: READ (15), nodeid: 4, insize: 80, pid: 24865
read[7] 4096 bytes from 0 flags: 0x8002
   read[7] 4096 bytes from 0
   unique: 69, error: -9 (Bad file descriptor), outsize: 16
unique: 70, opcode: FLUSH (25), nodeid: 4, insize: 64, pid: 24865
flush[7]
lock[7] F_SETLK F_UNLCK start: 0 len: 0 pid: 0
   unique: 70, success, outsize: 16
unique: 71, opcode: RELEASE (18), nodeid: 4, insize: 64, pid: 0
release[7] flags: 0x8002
   unique: 71, success, outsize: 16

Second run (same code, but when the file already exists)

unique: 72, opcode: LOOKUP (1), nodeid: 1, insize: 47, pid: 24874
LOOKUP /bentsi
getattr /bentsi
   NODEID: 4
   unique: 72, success, outsize: 144
unique: 73, opcode: OPEN (14), nodeid: 4, insize: 48, pid: 24874
open flags: 0x8002 /bentsi
   open[7] flags: 0x8002 /bentsi
   unique: 73, success, outsize: 32
unique: 74, opcode: GETXATTR (22), nodeid: 4, insize: 68, pid: 24874
getxattr /bentsi security.capability 0
   unique: 74, error: -61 (No data available), outsize: 16
unique: 75, opcode: WRITE (16), nodeid: 4, insize: 88, pid: 24874
write[7] 8 bytes to 0 flags: 0x8002
   write[7] 8 bytes to 0
   unique: 75, success, outsize: 24
unique: 76, opcode: GETATTR (3), nodeid: 4, insize: 56, pid: 24874
fgetattr[7] /bentsi
   unique: 76, success, outsize: 120
unique: 77, opcode: READ (15), nodeid: 4, insize: 80, pid: 24874
read[7] 4096 bytes from 0 flags: 0x8002
   read[7] 4096 bytes from 0
   unique: 77, success, outsize: 24
unique: 78, opcode: FLUSH (25), nodeid: 4, insize: 64, pid: 24874
flush[7]
lock[7] F_SETLK F_UNLCK start: 0 len: 0 pid: 0
   unique: 78, success, outsize: 16
unique: 79, opcode: RELEASE (18), nodeid: 4, insize: 64, pid: 0
release[7] flags: 0x8002
   unique: 79, success, outsize: 16