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| author | rsc <devnull@localhost> | 2005-01-14 03:45:44 +0000 |
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| committer | rsc <devnull@localhost> | 2005-01-14 03:45:44 +0000 |
| commit | 78e51a8c6678b6e3dff3d619aa786669f531f4bc (patch) | |
| tree | 015e00fde4fc837fd31b705e18d17dc913829388 /man/man9/open.html | |
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diff --git a/man/man9/open.html b/man/man9/open.html new file mode 100644 index 00000000..b893119b --- /dev/null +++ b/man/man9/open.html @@ -0,0 +1,154 @@ +<head> +<title>open(9P) - Plan 9 from User Space</title> +<meta content="text/html; charset=utf-8" http-equiv=Content-Type> +</head> +<body bgcolor=#ffffff> +<table border=0 cellpadding=0 cellspacing=0 width=100%> +<tr height=10><td> +<tr><td width=20><td> +<tr><td width=20><td><b>OPEN(9P)</b><td align=right><b>OPEN(9P)</b> +<tr><td width=20><td colspan=2> + <br> +<p><font size=+1><b>NAME </b></font><br> + +<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td> + + open, create – prepare a fid for I/O on an existing or new file<br> + +</table> +<p><font size=+1><b>SYNOPSIS </b></font><br> + +<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td> + + <i>size</i>[4] <tt><font size=+1>Topen</font></tt> <i>tag</i>[2] <i>fid</i>[4] <i>mode</i>[1]<br> + <i>size</i>[4] <tt><font size=+1>Ropen</font></tt> <i>tag</i>[2] <i>qid</i>[13] <i>iounit</i>[4] + <table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table> + + <i>size</i>[4] <tt><font size=+1>Tcreate</font></tt> <i>tag</i>[2] <i>fid</i>[4] <i>name</i>[<i>s</i>] <i>perm</i>[4] <i>mode</i>[1]<br> + <i>size</i>[4] <tt><font size=+1>Rcreate</font></tt> <i>tag</i>[2] <i>qid</i>[13] <i>iounit</i>[4]<br> + +</table> +<p><font size=+1><b>DESCRIPTION </b></font><br> + +<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td> + + The <tt><font size=+1>open</font></tt> request asks the file server to check permissions and + prepare a fid for I/O with subsequent <tt><font size=+1>read</font></tt> and <tt><font size=+1>write</font></tt> messages. + The <i>mode</i> field determines the type of I/O: 0 (called <tt><font size=+1>OREAD</font></tt> in + <tt><font size=+1><libc.h></font></tt>), 1 (<tt><font size=+1>OWRITE</font></tt>), 2 (<tt><font size=+1>ORDWR</font></tt>), and 3 (<tt><font size=+1>OEXEC</font></tt>) mean <i>read access, + write access, read and write access,</i> and <i>execute + access,</i> to be checked against the permissions for the file. In + addition, if <i>mode</i> has the <tt><font size=+1>OTRUNC</font></tt> (<tt><font size=+1>0x10</font></tt>) bit set, the file is to + be truncated, which requires write permission (if the file is + append-only, and permission is granted, the <tt><font size=+1>open</font></tt> succeeds but + the file will not be truncated); if the <i>mode</i> has the <tt><font size=+1>ORCLOSE</font></tt> (<tt><font size=+1>0x40</font></tt>) + bit set, the file is to be removed when the fid is clunked, which + requires permission to remove the file from its directory. All + other bits in <i>mode</i> should be zero. It is illegal to write a directory, + truncate it, or attempt to remove it on close. If the file is + marked for exclusive use (see <i>stat</i>(9P)), only one client can have + the + file open at any time. That is, after such a file has been opened, + further opens will fail until <i>fid</i> has been clunked. All these + permissions are checked at the time of the <tt><font size=+1>open</font></tt> request; subsequent + changes to the permissions of files do not affect the ability + to read, write, or remove an open file. + <table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table> + + The <tt><font size=+1>create</font></tt> request asks the file server to create a new file with + the <i>name</i> supplied, in the directory (<i>dir</i>) represented by <i>fid</i>, + and requires write permission in the directory. The owner of the + file is the implied user id of the request, the group of the file + is the same as <i>dir</i>, and the permissions are the value of + + <table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td> + + + <table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td> + + <tt><font size=+1>perm & (~0666 | (dir.perm & 0666)) <br> + </font></tt> + </table> + + </table> + if a regular file is being created and<br> + + <table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td> + + + <table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td> + + <tt><font size=+1>perm & (~0777 | (dir.perm & 0777)) <br> + </font></tt> + </table> + + </table> + if a directory is being created. This means, for example, that + if the <tt><font size=+1>create</font></tt> allows read permission to others, but the containing + directory does not, then the created file will not allow others + to read the file. + <table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table> + + Finally, the newly created file is opened according to <i>mode</i>, and + <i>fid</i> will represent the newly opened file. <i>Mode</i> is not checked + against the permissions in <i>perm</i>. The <i>qid</i> for the new file is returned + with the <tt><font size=+1>create</font></tt> reply message. + <table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table> + + Directories are created by setting the <tt><font size=+1>DMDIR</font></tt> bit (<tt><font size=+1>0x80000000</font></tt>) + in the <i>perm</i>. + <table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table> + + The names <tt><font size=+1>.</font></tt> and <tt><font size=+1>..</font></tt> are special; it is illegal to create files + with these names. + <table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table> + + It is an error for either of these messages if the fid is already + the product of a successful <tt><font size=+1>open</font></tt> or <tt><font size=+1>create</font></tt> message. + <table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table> + + An attempt to <tt><font size=+1>create</font></tt> a file in a directory where the given <i>name</i> + already exists will be rejected; in this case, the <i>fscreate</i> call + (see <a href="../man3/9pclient.html"><i>9pclient</i>(3)</a>) uses <tt><font size=+1>open</font></tt> with truncation. The algorithm used + by the <i>create</i> system call is: first walk to the directory to contain + the file. If that fails, return an error. Next <tt><font size=+1>walk</font></tt> to the + specified file. If the <tt><font size=+1>walk</font></tt> succeeds, send a request to <tt><font size=+1>open</font></tt> and + truncate the file and return the result, successful or not. If + the <tt><font size=+1>walk</font></tt> fails, send a create message. If that fails, it may be + because the file was created by another process after the previous + walk failed, so (once) try the <tt><font size=+1>walk</font></tt> and <tt><font size=+1>open</font></tt> again. + +</table> +<p><font size=+1><b>ENTRY POINTS </b></font><br> + +<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td> + + <i>Fsopen</i> and <i>fscreate</i> (see <a href="../man3/9pclient.html"><i>9pclient</i>(3)</a>) both generate <tt><font size=+1>open</font></tt> messages; + only <i>fscreate</i> generates a <tt><font size=+1>create</font></tt> message. The <tt><font size=+1>iounit</font></tt> associated + with an open file may be discovered by calling <i>fsiounit</i>. + <table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table> + + For programs that need atomic file creation, without the race + that exists in the <tt><font size=+1>open−create</font></tt> sequence described above, <i>fscreate</i> + does the following. If the <tt><font size=+1>OEXCL</font></tt> (<tt><font size=+1>0x1000</font></tt>) bit is set in the <i>mode</i> + for a <i>fscreate</i> call, the <tt><font size=+1>open</font></tt> message is not sent; the kernel + issues only the <tt><font size=+1>create</font></tt>. Thus, if the file exists, <i>fscreate + </i>will draw an error, but if it doesn’t and the <i>fscreate</i> call succeeds, + the process issuing the <i>fscreate</i> is guaranteed to be the one that + created the file.<br> + +</table> + +<td width=20> +<tr height=20><td> +</table> +<!-- TRAILER --> +<table border=0 cellpadding=0 cellspacing=0 width=100%> +<tr height=15><td width=10><td><td width=10> +<tr><td><td> +<center> +<a href="../../"><img src="../../dist/spaceglenda100.png" alt="Space Glenda" border=1></a> +</center> +</table> +<!-- TRAILER --> +</body></html> |