c++ - what is the purpose to set SOCK_CLOEXEC flag with accept4() same as O_CLOEXEC -


basically, need know purpose of setting sock_cloexec when sitting accept4(). how can check functionality of flag returned file descriptor accept.

accepted_fd =   accept4(sd, (struct sockaddr *)& tcp_remote, &size,  sock_cloexec);

the reason sock_cloexec exist avoid race condition between getting new socket accept , setting fd_cloexec flag afterwards.

normally if want file descriptor close-on-exec you'd first obtain file descriptor in way, call fcntl(fd, f_setfd, fd_cloexec). in threaded program there possibility race condition between getting file descriptor (in case accept) , setting cloexec flag. therefore linux has changed (if not all) system calls return new file descriptors accept flags tell kernel atomically set close-on-exec flag before making file descriptor valid. way race condition closed.

if wonder why close on exec exists, it's because in cases, when you're executing non-privileged programs privileged one, don't want file descriptors leak program.


Comments

Post a Comment

Popular posts from this blog

Android layout hidden on keyboard show -

i have strange problem layout. when tap on edittext , keyboard shown edittext stay on bottom , when tap on to hide keyboard , keyboard hides , edittext go should when want input text. when tap again, keyboard shown , edittext goes down behind keyboard... <relativelayout android:layout_width="match_parent" android:layout_height="match_parent" > <scrollview android:layout_width="match_parent" android:layout_height="fill_parent" android:above="@+id/rl_commands"> <textview android:layout_width="match_parent" android:layout_height="wrap_content"/> </scrollview> <relativelayout android:layout_width="match_parent android:layout_height="24dp" android:id="@+id/rl_commands" android:alignparentbottom="true">
Read more

google app engine - 403 Forbidden POST - Flask WTForms -

i have flask application running on google app engine. trying submit form built using wtform , keep getting following error. 403 forbidden: don't have permission access requested resource. either read-protected or not readable server. location.html (part of code) <form method=post action="/home/location"> .... <button type="submit" class="btn btn-primary" value="submit"> directions </button> </form> main.py @app.route('/home/location', methods=['post', 'get']) def location(): form = cfcdirections.direction(request.form) print(request.method) if request.method == 'post' , form.validate(): print("after if") directions = cfcdirections() street_no = directions.no street = directions.street suburb = directions.suburb postcode = directions.postcode
Read more

c - Why would PK11_GenerateRandom() return an error -8023? -

i looking through internet trying find source of pk11_generaterandom() function see why function fail. have program uses function when moved new flavor of linux, fails after forking ( fork() ) since not believe there problem nss, suspect doing incorrectly disregarded in older versions of linux new 1 there issue. the openssl package same on 'good' , 'bad' server: openssl 0.9.8e-fips-rhel5 01 jul nss rpm differs though. 'good' has nss-3.12.2.0-2.el5 and bas has version nss-3.15.3-4.el5_10 the 'good' server uses quite obsolete linux: linux 2.6.18-128.el5 #1 smp wed jan 21 08:45:05 est 2009 x86_64 x86_64 x86_64 gnu/linux enterprise linux enterprise linux server release 5.3 (carthage) red hat enterprise linux server release 5.3 (tikanga) the 'bad' server newer: linux bad 2.6.18-371.4.1.el5 #1 smp wed jan 29 11:05:49 pst 2014 x86_64 x86_64 x86_64 gnu/linux oracle linux server release 5.10 red hat enterprise linux server release
Read more