STAT(5)                                                   STAT(5)

          stat, wstat - inquire or change file attributes

          size[4] Tstat tag[2] fid[4]
          size[4] Rstat tag[2] stat[n]

          size[4] Twstat tag[2] fid[4] stat[n]
          size[4] Rwstat tag[2]

          The stat transaction inquires about the file identified by
          fid. The reply will contain a machine-independent directory
          entry, stat, laid out as follows:

               total byte count of the following data

               for kernel use

               for kernel use

               the type of the file (directory, etc.), represented as
               a bit vector corresponding to the high 8 bits of the
               file's mode word.

               version number for given path

               the file server's unique identification for the file

               permissions and flags

               last access time

               last modification time

               length of file in bytes

          name[ s ]
               file name; must be / if the file is the root directory
               of the server

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     STAT(5)                                                   STAT(5)

          uid[ s ]
               owner name

          gid[ s ]
               group name

          muid[ s ]
               name of the user who last modified the file

          Integers in this encoding are in little-endian order (least
          significant byte first).  The convM2D and convD2M routines
          (see fcall(2)) convert between directory entries and a C
          structure called a Dir.

          The mode contains permission bits as described in intro(5)
          and the following: 0x80000000 (DMDIR, this file is a direc-
          tory), 0x40000000 (DMAPPEND, append only), 0x20000000
          (DMEXCL, exclusive use), 0x04000000 (DMTMP, temporary);
          these are echoed in Qid.type.  Writes to append-only files
          always place their data at the end of the file; the offset
          in the write message is ignored, as is the OTRUNC bit in an
          open.  Exclusive use files may be open for I/O by only one
          fid at a time across all clients of the server.  If a second
          open is attempted, it draws an error.  Servers may implement
          a timeout on the lock on an exclusive use file: if the fid
          holding the file open has been unused for an extended period
          (of order at least minutes), it is reasonable to break the
          lock and deny the initial fid further I/O.  Temporary files
          are not included in nightly archives.

          The two time fields are measured in seconds since the epoch
          (Jan 1 00:00 1970 GMT).  The mtime field reflects the time
          of the last change of content (except when later changed by
          wstat).  For a plain file, mtime is the time of the most
          recent create, open with truncation, or write; for a direc-
          tory it is the time of the most recent remove, create, or
          wstat of a file in the directory.  Similarly, the atime
          field records the last read of the contents; also it is set
          whenever mtime is set.  In addition, for a directory, it is
          set by an attach, walk, or create, all whether successful or

          The muid field names the user whose actions most recently
          changed the mtime of the file.

          The length records the number of bytes in the file.  Direc-
          tories and most files representing devices have a conven-
          tional length of 0.

          The stat request requires no special permissions.

          The wstat request can change some of the file status

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     STAT(5)                                                   STAT(5)

          information.  The name can be changed by anyone with write
          permission in the parent directory; it is an error to change
          the name to that of an existing file.  The length can be
          changed (affecting the actual length of the file) by anyone
          with write permission on the file.  It is an error to
          attempt to set the length of a directory to a non-zero
          value, and servers may decide to reject length changes for
          other reasons.  The mode and mtime can be changed by the
          owner of the file or the group leader of the file's current
          group.  The directory bit cannot be changed by a wstat; the
          other defined permission and mode bits can.  The gid can be
          changed: by the owner if also a member of the new group; or
          by the group leader of the file's current group if also
          leader of the new group (see intro(5) for more information
          about permissions and users(6) for users and groups).  None
          of the other data can be altered by a wstat and attempts to
          change them will trigger an error.  In particular, it is
          illegal to attempt to change the owner of a file.  (These
          conditions may be relaxed when establishing the initial
          state of a file server; see fsconfig(8).)

          Either all the changes in wstat request happen, or none of
          them does: if the request succeeds, all changes were made;
          if it fails, none were.

          A wstat request can avoid modifying some properties of the
          file by providing explicit ``don't touch'' values in the
          stat data that is sent: zero-length strings for text values
          and the maximum unsigned value of appropriate size for inte-
          gral values.  As a special case, if all the elements of the
          directory entry in a Twstat message are ``don't touch'' val-
          ues, the server may interpret it as a request to guarantee
          that the contents of the associated file are committed to
          stable storage before the Rwstat message is returned.  (Con-
          sider the message to mean, ``make the state of the file
          exactly what it claims to be.'')

          A read of a directory yields an integral number of directory
          entries in the machine independent encoding given above (see

          Note that since the stat information is sent as a 9P
          variable-length datum, it is limited to a maximum of 65535

          Stat messages are generated by fstat and stat.

          Wstat messages are generated by fwstat and wstat.

          To make the contents of a directory, such as returned by

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     STAT(5)                                                   STAT(5)

          read(5), easy to parse, each directory entry begins with a
          size field.  For consistency, the entries in Twstat and
          Rstat messages also contain their size, which means the size
          appears twice.  For example, the Rstat message is formatted
          as ``(4+1+2+2+n)[4] Rstat tag[2] n[2] (n-2)[2] type[2]
          dev[4]...,'' where n is the value returned by convD2M.

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