From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael Kerrisk (man-pages)" Subject: Re: [PATCH] Fix readdir_r with long file names Date: Wed, 2 Mar 2016 11:39:06 +0100 Message-ID: <56D6C2CA.2020609@gmail.com> References: <51B0B39F.4060202@redhat.com> <51B0BD36.3030202@redhat.com> <20130607013024.GO29800@brightrain.aerifal.cx> <51B19203.3070307@redhat.com> <20130607144143.GQ29800@brightrain.aerifal.cx> <51B57E35.4080403@redhat.com> <51B65EA7.2020402@redhat.com> <20130611011324.GT29800@brightrain.aerifal.cx> <51B8702D.2060505@redhat.com> <20130813040038.GE21795@spoyarek.pnq.redhat.com> <520C88A6.9070501@redhat.com> <56D54DAD.1040306@gmail.com> <56D5CA79.9030204@redhat.com> <56D5F832.3070209@gmail.com> <56D5FB3D.5000306@redhat.com> <56D607BB.6080701@cs.ucla.edu> <56D614AA.7020500@redhat.com> <56D61A86.3050108@cs.ucla.edu> <56D620AA.40108@redhat.com> <56D624FE.1090702@cs.ucla.edu> <56D6294A.5040703@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <56D6294A.5040703-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> Sender: linux-man-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Florian Weimer , Paul Eggert , Siddhesh Poyarekar Cc: mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, Rich Felker , Carlos O'Donell , KOSAKI Motohiro , libc-alpha , Roland McGrath , linux-man List-Id: linux-man@vger.kernel.org On 03/02/2016 12:44 AM, Florian Weimer wrote: > On 03/02/2016 12:25 AM, Paul Eggert wrote: >=20 >>> And at the cost of >>> changing sizeof (struct dirent), which can't be a good thing. >> >> Any program that depends on sizeof (struct dirent) is broken already= , so >> this isn't that worrisome. >=20 > Just to be clear, you looked at the wrong struct dirent definition fo= r > GNU/Linux, there is a sysdeps override. >=20 > Right now, most programs relying on sizeof (struct dirent) work well = in > almost all cases. We really don't want to break that. There appears= to > be an overlap between these programs and users of readdir_r, so once = we > remove that from the API, we should have better story for struct dire= nt > declarators as well. So, it seems like much more could be said about this in documentation. How about the following text for the man page? DESCRIPTION [...] In the glibc implementation, the dirent structure is defined as follows: struct dirent { ino_t d_ino; /* Inode number */ off_t d_off; /* Not an offset; see below = */ unsigned short d_reclen; /* Length of this record */ unsigned char d_type; /* Type of file; not support= ed by all filesystem types *= / char d_name[256]; /* Null-terminated filename = */ }; [...] NOTES The d_name field The dirent structure definition shown above is taken from the glibc headers, and shows the d_name field with a fixed size. Warning: applications should avoid any dependence on the size of the dname field. POSIX defines it as char d_name[], a char=E2= =80=90 acter array of unspecified size, with at most NAME_MAX charac=E2= =80=90 ters preceding the terminating null byte ('\0'). POSIX.1 explicitly notes that this field should not be used as an lvalue. The standard also notes that the use of sizeof(d_name) (and by implication sizeof(struct dirent)) is incorrect; use strlen(d_name) instead. (On some systems, this field is defined as char d_name[1]!) Note that while the call fpathconf(fd, _PC_NAME_MAX) returns the value 255 for most filesystems, on some filesystems (e.g., CIFS, Windows SMB servers), the null-terminated filename that is (correctly) returned in d_name can actually exceed this size. (In such cases, the d_reclen field will contain a value that exceeds the size of the glibc dirent structure shown above.) Cheers, Michael --=20 Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/ -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html