From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Nazarewicz Subject: Re: Msync Invalid Arg Date: Tue, 29 Dec 2009 15:30:24 +0100 Message-ID: <87vdfphmyn.fsf@erwin.mina86.com> References: <22791256.21262087525518.JavaMail.root@wombat> Mime-Version: 1.0 Content-Type: multipart/signed; boundary="=-=-="; micalg=pgp-sha1; protocol="application/pgp-signature" Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:received:received:sender:from:to:cc:subject :references:x-url:x-pgp-fp:x-pgp:date:in-reply-to:message-id :user-agent:mime-version:content-type; bh=dEMYing2CqxoZ97wgIutMgkbB2n4potI+VjJiUWhxfc=; b=wgWDOv76l5xgFuGmGondQ00q8q6Pbr2WM+3UgBOVEQ+a5TBAQpnzTiIWToZ3QbjelZ duL/kQOvplk1kP+9O6KsySId10VsMYrDBVxnnf/oXtI8qrP+SSaRgx3hXDiJmCLVqVTN BGUD2zE73jWDMpA24swrsA5euVnU+6RJkDqj0= In-Reply-To: <22791256.21262087525518.JavaMail.root@wombat> (darshan ghumare's message of "Tue, 29 Dec 2009 06:52:05 -0500") Sender: linux-kernel-owner@vger.kernel.org List-ID: To: darshan.ghumare@gmail.com Cc: linux-c-programming@vger.kernel.org, linux-kernel@vger.kernel.org --=-=-= Content-Transfer-Encoding: quoted-printable darshan.ghumare@gmail.com writes: > Whne I try to execute following code I get "Invalid Argumemt" error > message in msync. /* Code rewritten to be shorter */ > #include > #include > #include > #include > #include > #include >=20 > #define DIE_IF(cnd, msg) do{ if (cnd) { perror(msg); return 1; } }while(0) >=20 > int main(void) > { > char data[20]; > void *addr; > int fd, ret; >=20 > fd =3D open("/dev/mem", O_RDWR | O_SYNC); > DIE_IF(fd < 0, "open"); >=20 > addr =3D mmap(0, 4096, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); > DIE_IF(addr =3D=3D MAP_FAILED, "mmap"); >=20 > strcpy(data, "Test Msg"); > ret =3D write(fd, data, strlen(data)); > DIE_IF(ret < 0, "write"); >=20 > ret =3D msync(addr, 4096, MS_SYNC); > DIE_IF(ret < 0, "msync"); >=20 > ret =3D lseek(fd, 0, SEEK_SET); > DIE_IF(ret < 0, "lseek"); >=20 > memset(data, 0, sizeof data); > ret =3D read(fd, data, sizeof data); > DIE_IF(ret < 0, "read"); > printf("Read: %s.\n", data); >=20 > return 0; > } The msync(2) fails because /dev/mem driver (drivers/char/mem.c) does not implement fsync file operation which is used by msync(2) system call. This sort of makes sense since there is no need to sync the /dev/mem file -- there is no backing storage on hard drive or anywhere, when you write data there you write directly to the memory and same goes for reading. Anyhow, I'm Ccing this to linux-kernel as maybe we need a dummy fsync operation for /dev/mem which would do nothing and return zero? =2D- Best regards, _ _ .o. | Liege of Serenly Enlightened Majesty of o' \,=3D./ `o ..o | Computer Science, Michal "mina86" Nazarewicz (o o) ooo +------ooO--(_)--Ooo-- --=-=-= Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.12 (GNU/Linux) iEYEARECAAYFAks6EokACgkQUyzLALfG3x4DJQCffDNvg08atG4/kAtlS3cNVARo cJYAniaVQS2Lo5kytNwCJe1JQh/j4uvN =2ln3 -----END PGP SIGNATURE----- --=-=-=--