Date: Fri, 26 Jul 2019 15:18:11 +0000 (UTC) From: Doug Moore <dougm@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r350359 - head/sbin/swapon Message-ID: <201907261518.x6QFIBPk059384@repo.freebsd.org>
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Author: dougm Date: Fri Jul 26 15:18:11 2019 New Revision: 350359 URL: https://svnweb.freebsd.org/changeset/base/350359 Log: Rewrite the comments that explain swapon_trim() to make them more comprehensible. Suggested by: rpokala Approved by: markj (mentor) Differential Revision: https://reviews.freebsd.org/D21034 Modified: head/sbin/swapon/swapon.c Modified: head/sbin/swapon/swapon.c ============================================================================== --- head/sbin/swapon/swapon.c Fri Jul 26 13:12:33 2019 (r350358) +++ head/sbin/swapon/swapon.c Fri Jul 26 15:18:11 2019 (r350359) @@ -746,9 +746,11 @@ swapon_trim(const char *name) off_t ioarg[2], sz; int error, fd; + /* Open a descriptor to create a consumer of the device. */ fd = open(name, O_WRONLY); if (fd < 0) errx(1, "Cannot open %s", name); + /* Find the device size. */ if (fstat(fd, &sb) < 0) errx(1, "Cannot stat %s", name); if (S_ISREG(sb.st_mode)) @@ -758,18 +760,22 @@ swapon_trim(const char *name) err(1, "ioctl(DIOCGMEDIASIZE)"); } else errx(1, "%s has an invalid file type", name); + /* Trim the device. */ ioarg[0] = 0; ioarg[1] = sz; if (ioctl(fd, DIOCGDELETE, ioarg) != 0) warn("ioctl(DIOCGDELETE)"); + /* Start using the device for swapping, creating a second consumer. */ + error = swapon(name); + /* - * swapon is invoked after trimming, so that the trimming doesn't happen - * after the device is in use for swapping, but before the fd is closed, - * for the benefit of geli, which could otherwise detach the device, - * before swapon, on close. + * Do not close the device until the swap pager has attempted to create + * another consumer. For GELI devices created with the 'detach -l' + * option, removing the last consumer causes the device to be detached + * - that is, to disappear. This ordering ensures that the device will + * not be detached until swapoff is called. */ - error = swapon(name); close(fd); return (error); }
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