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diff --git a/man-pages-posix-2013/man3p/readlink.3p b/man-pages-posix-2013/man3p/readlink.3p new file mode 100644 index 0000000..6bdf98f --- /dev/null +++ b/man-pages-posix-2013/man3p/readlink.3p @@ -0,0 +1,255 @@ +'\" et +.TH READLINK "3P" 2013 "IEEE/The Open Group" "POSIX Programmer's Manual" +.SH PROLOG +This manual page is part of the POSIX Programmer's Manual. +The Linux implementation of this interface may differ (consult +the corresponding Linux manual page for details of Linux behavior), +or the interface may not be implemented on Linux. + +.SH NAME +readlink, readlinkat +\(em read the contents of a symbolic link +.SH SYNOPSIS +.LP +.nf +#include <unistd.h> +.P +ssize_t readlink(const char *restrict \fIpath\fP, char *restrict \fIbuf\fP, + size_t \fIbufsize\fP); +ssize_t readlinkat(int \fIfd\fP, const char *restrict \fIpath\fP, + char *restrict \fIbuf\fP, size_t \fIbufsize\fP); +.fi +.SH DESCRIPTION +The +\fIreadlink\fR() +function shall place the contents of the symbolic link referred to by +.IR path +in the buffer +.IR buf +which has size +.IR bufsize . +If the number of bytes in the symbolic link is less than +.IR bufsize , +the contents of the remainder of +.IR buf +are unspecified. If the +.IR buf +argument is not large enough to contain the link content, the first +.IR bufsize +bytes shall be placed in +.IR buf . +.P +If the value of +.IR bufsize +is greater than +{SSIZE_MAX}, +the result is implementation-defined. +.P +Upon successful completion, +\fIreadlink\fR() +shall mark for update the last data access timestamp of the symbolic +link. +.P +The +\fIreadlinkat\fR() +function shall be equivalent to the +\fIreadlink\fR() +function except in the case where +.IR path +specifies a relative path. In this case the symbolic link whose content +is read is relative to the directory associated with the file +descriptor +.IR fd +instead of the current working directory. If the file descriptor was +opened without O_SEARCH, the function shall check whether directory +searches are permitted using the current permissions of the directory +underlying the file descriptor. If the file descriptor was opened with +O_SEARCH, the function shall not perform the check. +.P +If +\fIreadlinkat\fR() +is passed the special value AT_FDCWD in the +.IR fd +parameter, the current working directory shall be used and the behavior +shall be identical to a call to +\fIreadlink\fR(). +.SH "RETURN VALUE" +Upon successful completion, these functions shall return the count of +bytes placed in the buffer. Otherwise, these functions shall return a +value of \(mi1, leave the buffer unchanged, and set +.IR errno +to indicate the error. +.SH ERRORS +These functions shall fail if: +.TP +.BR EACCES +Search permission is denied for a component of the path prefix of +.IR path . +.TP +.BR EINVAL +The +.IR path +argument names a file that is not a symbolic link. +.TP +.BR EIO +An I/O error occurred while reading from the file system. +.TP +.BR ELOOP +A loop exists in symbolic links encountered during resolution of the +.IR path +argument. +.TP +.BR ENAMETOOLONG +.br +The length of a component of a pathname is longer than +{NAME_MAX}. +.TP +.BR ENOENT +A component of +.IR path +does not name an existing file or +.IR path +is an empty string. +.TP +.BR ENOTDIR +A component of the path prefix names an existing file that is neither +a directory nor a symbolic link to a directory, or the +.IR path +argument contains at least one non-\c +<slash> +character and ends with one or more trailing +<slash> +characters and the last pathname component names an existing file that +is neither a directory nor a symbolic link to a directory. +.br +.P +The +\fIreadlinkat\fR() +function shall fail if: +.TP +.BR EACCES +.IR fd +was not opened with O_SEARCH and the permissions of the directory +underlying +.IR fd +do not permit directory searches. +.TP +.BR EBADF +The +.IR path +argument does not specify an absolute path and the +.IR fd +argument is neither AT_FDCWD nor a valid file descriptor open for reading +or searching. +.TP +.BR ENOTDIR +The +.IR path +argument is not an absolute path and +.IR fd +is a file descriptor associated with a non-directory file. +.P +These functions may fail if: +.TP +.BR ELOOP +More than +{SYMLOOP_MAX} +symbolic links were encountered during resolution of the +.IR path +argument. +.TP +.BR ENAMETOOLONG +.br +The length of a pathname exceeds +{PATH_MAX}, +or pathname resolution of a symbolic link produced an intermediate +result with a length that exceeds +{PATH_MAX}. +.LP +.IR "The following sections are informative." +.SH EXAMPLES +.SS "Reading the Name of a Symbolic Link" +.P +The following example shows how to read the name of a symbolic link +named +.BR /modules/pass1 . +.sp +.RS 4 +.nf +\fB +#include <unistd.h> +.P +char buf[1024]; +ssize_t len; +\&... +if ((len = readlink("/modules/pass1", buf, sizeof(buf)-1)) != -1) + buf[len] = '\e0'; +.fi \fR +.P +.RE +.SH "APPLICATION USAGE" +Conforming applications should not assume that the returned contents of +the symbolic link are null-terminated. +.SH RATIONALE +The type associated with +.IR bufsiz +is a +.BR size_t +in order to be consistent with both the ISO\ C standard and the definition of +\fIread\fR(). +The behavior specified for +\fIreadlink\fR() +when +.IR bufsiz +is zero represents historical practice. For this case, the standard +developers considered a change whereby +\fIreadlink\fR() +would return the number of non-null bytes contained in the symbolic +link with the buffer +.IR buf +remaining unchanged; however, since the +.BR stat +structure member +.IR st_size +value can be used to determine the size of buffer necessary to contain +the contents of the symbolic link as returned by +\fIreadlink\fR(), +this proposal was rejected, and the historical practice retained. +.P +The purpose of the +\fIreadlinkat\fR() +function is to read the content of symbolic links in directories other +than the current working directory without exposure to race conditions. +Any part of the path of a file could be changed in parallel to a call +to +\fIreadlink\fR(), +resulting in unspecified behavior. By opening a file descriptor for +the target directory and using the +\fIreadlinkat\fR() +function it can be guaranteed that the symbolic link read is located +relative to the desired directory. +.SH "FUTURE DIRECTIONS" +None. +.SH "SEE ALSO" +.IR "\fIfstatat\fR\^(\|)", +.IR "\fIsymlink\fR\^(\|)" +.P +The Base Definitions volume of POSIX.1\(hy2008, +.IR "\fB<unistd.h>\fP" +.SH COPYRIGHT +Portions of this text are reprinted and reproduced in electronic form +from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology +-- Portable Operating System Interface (POSIX), The Open Group Base +Specifications Issue 7, Copyright (C) 2013 by the Institute of +Electrical and Electronics Engineers, Inc and The Open Group. +(This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the +event of any discrepancy between this version and the original IEEE and +The Open Group Standard, the original IEEE and The Open Group Standard +is the referee document. The original Standard can be obtained online at +http://www.unix.org/online.html . + +Any typographical or formatting errors that appear +in this page are most likely +to have been introduced during the conversion of the source files to +man page format. To report such errors, see +https://www.kernel.org/doc/man-pages/reporting_bugs.html . |