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fdopendir(3p) — Linux manual page

PROLOG \|NAME \|SYNOPSIS \|DESCRIPTION \|RETURN VALUE \|ERRORS \|EXAMPLES \|APPLICATION USAGE \|RATIONALE \|FUTURE DIRECTIONS \|SEE ALSO \|COPYRIGHT

FDOPENDIR(3P)           POSIX Programmer's ManualFDOPENDIR(3P)

PROLOG top

       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.

NAME top

       fdopendir, opendir — open directory associated with file       descriptor

SYNOPSIS top

       #include <dirent.h>       DIR *fdopendir(intfd);       DIR *opendir(const char *dirname);

DESCRIPTION top

       Thefdopendir() function shall be equivalent to theopendir()       function except that the directory is specified by a file       descriptor rather than by a name. The file offset associated with       the file descriptor at the time of the call determines which       entries are returned.       Upon successful return fromfdopendir(), the file descriptor is       under the control of the system, and if any attempt is made to       close the file descriptor, or to modify the state of the       associated description, other than by means ofclosedir(),readdir(),readdir_r(),rewinddir(), orseekdir(), the behavior is       undefined. Upon callingclosedir() the file descriptor shall be       closed.       It is unspecified whether the FD_CLOEXEC flag will be set on the       file descriptor by a successful call tofdopendir().       Theopendir() function shall open a directory stream corresponding       to the directory named by thedirname argument. The directory       stream is positioned at the first entry. If the typeDIRis       implemented using a file descriptor, applications shall only be       able to open up to a total of {OPEN_MAX} files and directories.       If the typeDIRis implemented using a file descriptor, the       descriptor shall be obtained as if the O_DIRECTORY flag was passed       toopen().

RETURN VALUE top

       Upon successful completion, these functions shall return a pointer       to an object of typeDIR.  Otherwise, these functions shall return       a null pointer and seterrno to indicate the error.

ERRORS top

       Thefdopendir() function shall fail if:EBADFThefd argument is not a valid file descriptor open for              reading.ENOTDIR              The descriptorfd is not associated with a directory.       Theopendir() function shall fail if:EACCESSearch permission is denied for the component of the path              prefix ofdirname or read permission is denied fordirname.ELOOPA loop exists in symbolic links encountered during              resolution of thedirname argument.ENAMETOOLONG              The length of a component of a pathname is longer than              {NAME_MAX}.ENOENTA component ofdirname does not name an existing directory              ordirname is an empty string.ENOTDIR              A component ofdirname names an existing file that is              neither a directory nor a symbolic link to a directory.       Theopendir() function may fail if:ELOOPMore than {SYMLOOP_MAX} symbolic links were encountered              during resolution of thedirname argument.EMFILEAll file descriptors available to the process are currently              open.ENAMETOOLONG              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}.ENFILEToo many files are currently open in the system.The following sections are informative.

EXAMPLES top

Open a Directory Stream       The following program fragment demonstrates how theopendir()       function is used.           #include <dirent.h>           ...               DIR *dir;               struct dirent *dp;           ...               if ((dir = opendir (".")) == NULL) {                   perror ("Cannot open .");                   exit (1);               }               while ((dp = readdir (dir)) != NULL) {           ...Find And Open a File       The following program searches through a given directory looking       for files whose name does not begin with a dot and whose size is       larger than 1 MiB.           #include <stdio.h>           #include <dirent.h>           #include <fcntl.h>           #include <sys/stat.h>           #include <stdint.h>           #include <stdlib.h>           #include <unistd.h>           int           main(int argc, char *argv[])           {               struct stat statbuf;               DIR *d;               struct dirent *dp;               int dfd, ffd;               if ((d = fdopendir((dfd = open("./tmp", O_RDONLY)))) == NULL) {                   fprintf(stderr, "Cannot open ./tmp directory\n");                   exit(1);               }               while ((dp = readdir(d)) != NULL) {                   if (dp->d_name[0] == '.')                       continue;                   /* there is a possible race condition here as the file                    * could be renamed between the readdir and the open */                   if ((ffd = openat(dfd, dp->d_name, O_RDONLY)) == -1) {                       perror(dp->d_name);                       continue;                   }                   if (fstat(ffd, &statbuf) == 0 && statbuf.st_size > (1024*1024)) {                       /* found it ... */                       printf("%s: %jdK\n", dp->d_name,                           (intmax_t)(statbuf.st_size / 1024));                   }                   close(ffd);               }               closedir(d); // note this implicitly closes dfd               return 0;           }

APPLICATION USAGE top

       Theopendir() function should be used in conjunction withreaddir(),closedir(), andrewinddir() to examine the contents of       the directory (see the EXAMPLES section inreaddir(3p)).  This       method is recommended for portability.

RATIONALE top

       The purpose of thefdopendir() function is to enable opening files       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 toopendir(), resulting in       unspecified behavior.       Based on historical implementations, the rules about file       descriptors apply to directory streams as well. However, this       volume of POSIX.1‐2017 does not mandate that the directory stream       be implemented using file descriptors. The description ofclosedir() clarifies that if a file descriptor is used for the       directory stream, it is mandatory thatclosedir() deallocate the       file descriptor. When a file descriptor is used to implement the       directory stream, it behaves as if the FD_CLOEXEC had been set for       the file descriptor.       The directory entries for dot and dot-dot are optional. This       volume of POSIX.1‐2017 does not provide a way to testa priori for       their existence because an application that is portable must be       written to look for (and usually ignore) those entries. Writing       code that presumes that they are the first two entries does not       always work, as many implementations permit them to be other than       the first two entries, with a ``normal'' entry preceding them.       There is negligible value in providing a way to determine what the       implementation does because the code to deal with dot and dot-dot       must be written in any case and because such a flag would add to       the list of those flags (which has proven in itself to be       objectionable) and might be abused.       Since the structure and buffer allocation, if any, for directory       operations are defined by the implementation, this volume of       POSIX.1‐2017 imposes no portability requirements for erroneous       program constructs, erroneous data, or the use of unspecified       values such as the use or referencing of adirp value or adirent       structure value after a directory stream has been closed or after       afork() or one of theexec function calls.

FUTURE DIRECTIONS top

       None.

COPYRIGHT top

       Portions of this text are reprinted and reproduced in electronic       form from IEEE Std 1003.1-2017, Standard for Information       Technology -- Portable Operating System Interface (POSIX), The       Open Group Base Specifications Issue 7, 2018 Edition, Copyright       (C) 2018 by the Institute of Electrical and Electronics Engineers,       Inc and The Open Group.  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 athttp://www.opengroup.org/unix/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, seehttps://www.kernel.org/doc/man-pages/reporting_bugs.html .IEEE/The Open Group                2017FDOPENDIR(3P)

Pages that refer to this page:dirent.h(0p), closedir(3p), dirfd(3p), fstatat(3p), ftw(3p), glob(3p), nftw(3p), open(3p), opendir(3p), readdir(3p), rewinddir(3p), seekdir(3p), symlink(3p), telldir(3p)