Monitors changes in mounts (/proc/mounts file).

mountmon.py

import re
import logging
from collections import OrderedDict

import gevent

log = logging.getLogger(__name__)
logging.basicConfig(
    format="%(asctime)s %(name)s %(levelname)s %(message)s",
    level=logging.INFO
)

# Checking frequency in seconds.
frequency = 0.1

def get_current_mounts():
    """ Get the currently mounted filesystems.

    Reading from /proc/mounts is only consistent within a single read(3) call.
    Unfortuately, the maximum amount of data you can get from this file in a
    single call is hardcoded by the kernel to PAGE_SIZE (4096 bytes on x86). As
    a consequence, there is no way to read from this file in a consistent
    manner.

    As a (arguably ugly) workaround, we read from /proc/mounts until we get two
    reads in a row that are consistent with each other.

    We also acquire the volume lock, so that at least we are not trying to run
    mount/umount concurrently with reading /proc/mounts.
    """

    previous_data = None
    data = None
    while True:
        with open("/proc/mounts", "rb") as f:
            data = f.read()
        if data == previous_data:
            break
        else:
            previous_data = data

    mounts = OrderedDict()
    for line in data.split("\n"):
        line = line.strip()
        if len(line) == 0:
            continue

        info = {}
        cols = re.split("\s+", line)

        info["source"] = cols[0].rstrip("/")
        info["mount-point"] = cols[1]
        info["fs-type"] = cols[2]
        info["options"] = cols[3]
        info["dump"] = cols[4]
        info["pass"] = cols[5]

        mounts[info["mount-point"]] = info

    return mounts

previous = OrderedDict()
def monitor():
    global previous
    while True:
        current = get_current_mounts()

        for path, info in current.iteritems():
            if path not in previous:
                 log.info("mount: %s", path)
            else:
                if info["options"] != previous[path]["options"]:
                    log.info(
                        "options: %s -> %s",
                        previous[path]["options"],
                        info["options"]
                    )

        for path, info in previous.iteritems():
            if path not in current:
                 log.info("umount: %s", path)

        previous = current
        gevent.sleep(frequency)

g = gevent.spawn(monitor)
g.join()