It was introduced in Linux 2.6.39, glibc 2.14 and allows to obtain
file descriptors without actually opening files. Thus made it possible
to traverse path with openat() syscalls without the need to have read
permissions for path components. It is effectively emulates O_SEARCH
which is missing on Linux.
O_PATH is used in combination with O_RDONLY. The last one is ignored
if O_PATH is used, but it allows nginx to not fail when it was built on
modern system (i.e. glibc 2.14+) and run with a kernel older than 2.6.39.
Then O_PATH is unknown to the kernel and ignored, while O_RDONLY is used.
Sadly, fstat() is not working with O_PATH descriptors till Linux 3.6.
As a workaround we fallback to fstatat() with the AT_EMPTY_PATH flag
that was introduced at the same time as O_PATH.
HP-UX needs _HPUX_ALT_XOPEN_SOCKET_API to be defined to be able to
use various POSIX versions of networking functions. Notably sendmsg()
resulted in "sendmsg() failed (9: Bad file number)" alerts without it.
See xopen_networking(7) for more details.
This fixes alignment problems observerd on ARMs, and likely also needed
for MIPSes. Unless we know alignment is not required just assume we
need 16, which appears to be safe default for all architectures.
See here for details:
http://mailman.nginx.org/pipermail/nginx/2012-June/034139.html
Catch up with new Linux version numbering scheme as announced at [1] and
suppress unrecognized versions to actually use default 0.
[1] https://lkml.org/lkml/2011/5/29/204
*) Feature: the ngx_http_addition_filter_module.
*) Feature: the "proxy_pass" and "fastcgi_pass" directives may be used
inside the "if" block.
*) Feature: the "proxy_ignore_client_abort" and
"fastcgi_ignore_client_abort" directives.
*) Feature: the "$request_completion" variable.
*) Feature: the ngx_http_perl_module supports the $r->request_method
and $r->remote_addr.
*) Feature: the ngx_http_ssi_module supports the "elif" command.
*) Bugfix: the "\/" string in the expression of the "if" command of the
ngx_http_ssi_module was treated incorrectly.
*) Bugfix: in the regular expressions in the "if" command of the
ngx_http_ssi_module.
*) Bugfix: if the relative path was specified in the
"client_body_temp_path", "proxy_temp_path", "fastcgi_temp_path", and
"perl_modules" directives, then the directory was used relatively to
a current path but not to a server prefix.
Valentin Bartenev
Ruslan Ermilov
Maxim Dounin
Maxim Konovalov
Igor Sysoev