172 lines
6.0 KiB
HTML
172 lines
6.0 KiB
HTML
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<html>
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<head>
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<title>execv</title>
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<link rel="stylesheet" type="text/css" media="all" href="../man.css">
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</head>
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<body bgcolor=#ffffff>
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<h2 align=center>execv</h2>
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<h4 align=center>OS/161 Reference Manual</h4>
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<h3>Name</h3>
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<p>
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execv - execute a program
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</p>
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<h3>Library</h3>
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<p>
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Standard C Library (libc, -lc)
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</p>
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<h3>Synopsis</h3>
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<p>
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<tt>#include <unistd.h></tt><br>
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<br>
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<tt>int</tt><br>
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<tt>execv(const char *</tt><em>program</em><tt>,
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char **</tt><em>args</em><tt>);</tt>
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<br>
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<tt>int</tt><br>
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<tt>execve(const char *</tt><em>program</em><tt>,
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char **</tt><em>args</em>,
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char **</tt><em>environ</em><tt>);</tt>
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</p>
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<h3>Description</h3>
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<p>
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<tt>execv</tt> replaces the currently executing program with a newly
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loaded program image. This occurs within one process; the process id
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is unchanged.
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</p>
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<p>
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The pathname of the program to run is passed as <em>program</em>. The
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<em>args</em> argument is an array of 0-terminated strings. The array
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itself should be terminated by a <tt>NULL</tt> pointer.
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</p>
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<p>
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The argument strings should be copied into the new process as the new
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process's <tt>argv[]</tt> array. In the new process,
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<tt>argv[argc]</tt> must be <tt>NULL</tt>.
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</p>
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<p>
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By convention, <tt>argv[0]</tt> in new processes contains the name
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that was used to invoke the program. This is not necessarily the same
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as <em>program</em>, and furthermore is only a convention and should
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not be enforced by the kernel.
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</p>
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<p>
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The process file table and current working directory are not modified
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by <tt>execv</tt>.
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</p>
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<p>
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The <tt>execve</tt> call is the same as <tt>execv</tt> except that a
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<tt>NULL</tt>-terminated list of environment strings (of the form
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<tt>var=value</tt>) is also passed through. In Unix, <tt>execv</tt> is
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a small wrapper for <tt>execve</tt> that supplies the current process
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environment. <b>In OS/161, <tt>execv</tt> is the primary exec call and
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<tt>execve</tt> is not supported or needed</b> unless you put in extra
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work to implement it.
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</p>
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<p>
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The maximum total size of the argv (and environment, if any) data is
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given by the system constant <tt>ARG_MAX</tt>. This comes set to 64K
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by default. You may change this limit, but don't reduce it without
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asking your course staff. The fact that argv blocks can be large is
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part of the design problem; while it's possible to set the limit to 4K
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and still have most things work, you are probably supposed to put at
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least some thought into engineering a real solution. (One problem to
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consider is that after the system has been up a while and system
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memory starts to become fragmented, you still need to be able to
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allocate enough memory to handle exec. Another is to make sure the
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system doesn't choke if too many processes are trying to exec at
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once. There are lots of ways to tackle this; be creative.)
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</p>
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<p>
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Whether the size of the pointers appearing in the <tt>argv</tt> array
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count towards the <tt>ARG_MAX</tt> limit is implementation-defined.
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Either way it should be possible to pass a lot of small arguments
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without bumping into some other limit on the number of pointers.
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</p>
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<h3>Return Values</h3>
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<p>
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On success, <tt>execv</tt> does not return; instead, the new program
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begins executing. On failure, <tt>execv</tt> returns -1, and sets
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<A HREF=errno.html>errno</A> to a suitable error code for the error
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condition encountered.
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</p>
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<h3>Errors</h3>
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<p>
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The following error codes should be returned under the conditions
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given. Other error codes may be returned for other errors not
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mentioned here.
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<table width=90%>
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<tr><td width=5% rowspan=9> </td>
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<td width=10% valign=top>ENODEV</td>
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<td>The device prefix of <em>program</em> did
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not exist.</td></tr>
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<tr><td valign=top>ENOTDIR</td>
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<td>A non-final component of <em>program</em>
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was not a directory.</td></tr>
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<tr><td valign=top>ENOENT</td>
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<td><em>program</em> did not exist.</td></tr>
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<tr><td valign=top>EISDIR</td>
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<td><em>program</em> is a directory.</td></tr>
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<tr><td valign=top>ENOEXEC</td>
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<td><em>program</em> is not in a recognizable
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executable file format, was for the
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wrong platform, or contained invalid
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fields.</td></tr>
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<tr><td valign=top>ENOMEM</td>
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<td>Insufficient virtual memory is available.</td></tr>
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<tr><td valign=top>E2BIG</td>
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<td>The total size of the argument strings
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exceeeds <tt>ARG_MAX</tt>.</td></tr>
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<tr><td valign=top>EIO</td>
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<td>A hard I/O error occurred.</td></tr>
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<tr><td valign=top>EFAULT</td>
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<td>One of the arguments is an invalid
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pointer.</td></tr>
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</table>
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</p>
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</body>
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</html>
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