Date: Fri, 23 Jun 2006 18:57:41 +0400 From: Stanislav Sedov <stas@310.ru> To: freebsd-hackers@freebsd.org Subject: Re: Simple question about mmap() system call Message-ID: <20060623185741.71a441ec.stas@310.ru> In-Reply-To: <20060623173723.H39481@atlantis.atlantis.dp.ua> References: <20060623173723.H39481@atlantis.atlantis.dp.ua>
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On Fri, 23 Jun 2006 17:47:57 +0300 (EEST)
Dmitry Pryanishnikov <dmitry@atlantis.dp.ua> wrote:
> Hello!
>=20
> I'm writing an utility that should examine some bytes of a large file
> and modify them - that't all. I've decided to mmap() the file:
>=20
> void *diskp;
>=20
> if ((fd=3Dopen(argv[1], O_RDWR)) =3D=3D -1)
> err(EX_NOINPUT, "Can't open %s for readind and writing", argv[1]=
);
>=20
> if ((diskp=3Dmmap(NULL, 512,
> PROT_READ | PROT_WRITE, 0, fd, 0)) =3D=3D MAP_FAILED)
> err(EX_IOERR, "Can't mmap() file");
>=20
> printf("<%c>\n",* (char *)diskp);
> * (char *)diskp =3D '!';
>=20
> if (msync(diskp, 0, MS_SYNC) || close(fd))
> err(EX_IOERR, "Error closing file");
>=20
> All proceeds w/o errors with the sample (2 bytes long) file, printf()
> shows actual first byte of my file. But modification doesn't get written =
back=20
> to the disk, file contents are unchanged after execution of my code. I'm =
sure=20
> I'm overlooking something very basic and stupid, but can't find what exac=
tly.
>=20
munmap(2)?
--=20
Stanislav Sedov MBSD labs, Inc. <ssedov@mbsd.msk.ru>
=F2=CF=D3=D3=C9=D1, =ED=CF=D3=CB=D7=C1 http://mbsd.msk.ru
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