Reword a little to allow for the fact that there are now
*two* reasons to consider using this flag.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Since introduction of MAP_SHARED_VALIDATE, in case flags contain
both MAP_PRIVATE and MAP_SHARED, mmap() doesn't fail with EINVAL,
it succeeds.
The reason for that is that MAP_SHARED_VALIDATE is in fact equal
to MAP_PRIVATE | MAP_SHARED.
This is intended behavior, see:
https://lwn.net/Articles/758594/https://lwn.net/Articles/758598/
Signed-off-by: Nikola Forró <nforro@redhat.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Quoting Branden:
*roff escape sequences may sometimes look like C escapes, but that
is misleading. *roff is in part a macro language and that means
recursive expansion to arbitrary depths.
You can get away with "\\" in a context where no macro expansion
is taking place, but try to spell a literal backslash this way in
the argument to a macro and you will likely be unhappy with
results.
Try viewing the attached file with "man -l".
"\e" is the preferred and portable way to get a portable "escape
literal" going back to CSTR #54, the original Bell Labs troff
paper.
groff(7) discusses the issue:
\\ reduces to a single backslash; useful to delay its
interpretation as escape character in copy mode. For a
printable backslash, use \e, or even better \[rs], to be
independent from the current escape character.
As of groff 1.22.4, groff_man(7) does as well:
\e Widely used in man pages to represent a backslash output
glyph. It works reliably as long as the .ec request is
not used, which should never happen in man pages, and it
is slightly more portable than the more exact ‘\(rs’
(“reverse solidus”) escape sequence.
People not concerned with portability to extremely old troffs should
probably just use \(rs (or \[rs]), as it means "the backslash
glyph", not "the glyph corresponding to whatever the current escape
character is".
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
The current manpage reads to me as if the kernel will always pick
a free space close to the requested address, but that's not the
case:
mmap(0x600000000000, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS,
-1, 0) = 0x600000000000
mmap(0x600000000000, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS,
-1, 0) = 0x7f5042859000
You can also see this in the various implementations of
->get_unmapped_area() - if the specified address isn't available,
the kernel basically ignores the hint (apart from the 5level
paging hack).
Clarify how this works a bit.
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
I regularly see excessive fd usage bugs (or even leaks) caused by
people who think they need to keep the fd open as long as the
mapping exists.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This text has become rather long, making it it somewhat
unwieldy in the discussion of the mmap() flags. Therefore,
move it to NOTES, with a pointer in DESCRIPTION referring
the reader to NOTES.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Change "extremely hazardous" to "hazardous". The former phrasing
is a little overwrought; on its own "hazardous" is enough to
convey the sense of danger.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Clarify that MAP_FIXED is appropriate if the specified address
range has been reserved using an existing mapping, but shouldn't
be used otherwise.
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
In Linux 2..0, do_mmap() had the following check:
if (flags & MAP_DENYWRITE) {
if (file->f_inode->i_writecount > 0)
return -ETXTBSY;
}
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
4.17+ kernels offer a new MAP_FIXED_NOREPLACE flag which allows
the caller to atomically probe for a given address range.
[wording heavily updated by John Hubbard]
Cowritten-by: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
One last thing: reading through this, I think it might need a
wording fix (this is my fault), in order to avoid implying that
brk() or malloc() use dlopen().
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Michael Kerrisk