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Rewrite the comments that explain swapon_trim() to make them more

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comprehensible.

Suggested by: rpokala
Approved by: markj (mentor)
Differential Revision: https://reviews.freebsd.org/D21034
This commit is contained in:
dougm 2019-07-26 15:18:11 +00:00
parent 9563c2d6d7
commit bdfb9f2d6b
1 changed files with 12 additions and 6 deletions
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18
sbin/swapon/swapon.c
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@ -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)");
/*
* 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.
*/
/* Start using the device for swapping, creating a second consumer. */
error = swapon(name);
/*
* 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.
*/
close(fd);
return (error);
}