Re: svn commit: r196558 - head/usr.bin/look
On Saturday 29 August 2009 4:35:16 pm Alan Cox wrote: John Baldwin wrote: On Tuesday 25 August 2009 11:30:06 pm Colin Percival wrote: Author: cperciva Date: Wed Aug 26 03:30:06 2009 New Revision: 196558 URL: http://svn.freebsd.org/changeset/base/196558 Log: Don't try to mmap the contents of empty files. This behaviour was harmless prior to r195693, since historical behaviour of mmap(2) was to silently ignore length-zero mmap requests; but mmap now returns EINVAL, which caused look(1) to emit an error message and fail. FWIW, it did not silently ignore the request. Instead it rounded the size up to a page and mapped a page of data. However, if you then passed that pointer with a length of 0 to munmap() munmap() would fail. I don't believe that your claim is correct; round_page(0) == 0. Thus, the value of size that would be passed to vm_mmap() would be 0, which would cause it to immediately return 0, indicating success. In this case, I believe that the virtual address that would be returned by mmap(2) would always be the hint address for where it should start looking for free space, which would be the end of the heap/data segment, unless the application specified its own hint. In short, and the reason why I'm correcting you here, is to make clear that we needn't worry about earlier versions of FreeBSD that don't implement this change leaking or wasting memory from misuse of mmap(2) in this way. Yes, I think you are correct. -- John Baldwin ___ svn-src-all@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to svn-src-all-unsubscr...@freebsd.org
Re: svn commit: r196558 - head/usr.bin/look
John Baldwin wrote: On Tuesday 25 August 2009 11:30:06 pm Colin Percival wrote: Author: cperciva Date: Wed Aug 26 03:30:06 2009 New Revision: 196558 URL: http://svn.freebsd.org/changeset/base/196558 Log: Don't try to mmap the contents of empty files. This behaviour was harmless prior to r195693, since historical behaviour of mmap(2) was to silently ignore length-zero mmap requests; but mmap now returns EINVAL, which caused look(1) to emit an error message and fail. FWIW, it did not silently ignore the request. Instead it rounded the size up to a page and mapped a page of data. However, if you then passed that pointer with a length of 0 to munmap() munmap() would fail. I don't believe that your claim is correct; round_page(0) == 0. Thus, the value of size that would be passed to vm_mmap() would be 0, which would cause it to immediately return 0, indicating success. In this case, I believe that the virtual address that would be returned by mmap(2) would always be the hint address for where it should start looking for free space, which would be the end of the heap/data segment, unless the application specified its own hint. In short, and the reason why I'm correcting you here, is to make clear that we needn't worry about earlier versions of FreeBSD that don't implement this change leaking or wasting memory from misuse of mmap(2) in this way. Alan ___ svn-src-all@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to svn-src-all-unsubscr...@freebsd.org
Re: svn commit: r196558 - head/usr.bin/look
On Tuesday 25 August 2009 11:30:06 pm Colin Percival wrote: Author: cperciva Date: Wed Aug 26 03:30:06 2009 New Revision: 196558 URL: http://svn.freebsd.org/changeset/base/196558 Log: Don't try to mmap the contents of empty files. This behaviour was harmless prior to r195693, since historical behaviour of mmap(2) was to silently ignore length-zero mmap requests; but mmap now returns EINVAL, which caused look(1) to emit an error message and fail. FWIW, it did not silently ignore the request. Instead it rounded the size up to a page and mapped a page of data. However, if you then passed that pointer with a length of 0 to munmap() munmap() would fail. -- John Baldwin ___ svn-src-all@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to svn-src-all-unsubscr...@freebsd.org
svn commit: r196558 - head/usr.bin/look
Author: cperciva
Date: Wed Aug 26 03:30:06 2009
New Revision: 196558
URL: http://svn.freebsd.org/changeset/base/196558
Log:
Don't try to mmap the contents of empty files. This behaviour was harmless
prior to r195693, since historical behaviour of mmap(2) was to silently
ignore length-zero mmap requests; but mmap now returns EINVAL, which caused
look(1) to emit an error message and fail.
Among other things, this makes `freebsd-update fetch` on a newly installed
8.0-BETA3 system print bogus warning messages.
MFC after:3 days
Modified:
head/usr.bin/look/look.c
Modified: head/usr.bin/look/look.c
==
--- head/usr.bin/look/look.cTue Aug 25 21:51:47 2009(r196557)
+++ head/usr.bin/look/look.cWed Aug 26 03:30:06 2009(r196558)
@@ -140,6 +140,10 @@ main(int argc, char *argv[])
err(2, %s, file);
if (sb.st_size SIZE_T_MAX)
errx(2, %s: %s, file, strerror(EFBIG));
+ if (sb.st_size == 0) {
+ close(fd);
+ continue;
+ }
if ((front = mmap(NULL, (size_t)sb.st_size, PROT_READ,
MAP_SHARED, fd, (off_t)0)) == MAP_FAILED)
err(2, %s, file);
back = front + sb.st_size;
___
svn-src-all@freebsd.org mailing list
http://lists.freebsd.org/mailman/listinfo/svn-src-all
To unsubscribe, send any mail to svn-src-all-unsubscr...@freebsd.org
