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45 lines
2.7 KiB
Go
45 lines
2.7 KiB
Go
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// Package mountinfo provides a set of functions to retrieve information about OS mounts.
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//
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// Currently it supports Linux. For historical reasons, there is also some support for FreeBSD and OpenBSD,
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// and a shallow implementation for Windows, but in general this is Linux-only package, so
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// the rest of the document only applies to Linux, unless explicitly specified otherwise.
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//
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// In Linux, information about mounts seen by the current process is available from
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// /proc/self/mountinfo. Note that due to mount namespaces, different processes can
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// see different mounts. A per-process mountinfo table is available from /proc/<PID>/mountinfo,
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// where <PID> is a numerical process identifier.
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//
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// In general, /proc is not a very efficient interface, and mountinfo is not an exception.
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// For example, there is no way to get information about a specific mount point (i.e. it
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// is all-or-nothing). This package tries to hide the /proc ineffectiveness by using
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// parse filters while reading mountinfo. A filter can skip some entries, or stop
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// processing the rest of the file once the needed information is found.
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//
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// For mountinfo filters that accept path as an argument, the path must be absolute,
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// having all symlinks resolved, and being cleaned (i.e. no extra slashes or dots).
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// One way to achieve all of the above is to employ filepath.Abs followed by
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// filepath.EvalSymlinks (the latter calls filepath.Clean on the result so
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// there is no need to explicitly call filepath.Clean).
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//
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// NOTE that in many cases there is no need to consult mountinfo at all. Here are some
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// of the cases where mountinfo should not be parsed:
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//
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// 1. Before performing a mount. Usually, this is not needed, but if required (say to
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// prevent over-mounts), to check whether a directory is mounted, call os.Lstat
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// on it and its parent directory, and compare their st.Sys().(*syscall.Stat_t).Dev
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// fields -- if they differ, then the directory is the mount point. NOTE this does
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// not work for bind mounts. Optionally, the filesystem type can also be checked
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// by calling unix.Statfs and checking the Type field (i.e. filesystem type).
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//
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// 2. After performing a mount. If there is no error returned, the mount succeeded;
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// checking the mount table for a new mount is redundant and expensive.
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//
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// 3. Before performing an unmount. It is more efficient to do an unmount and ignore
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// a specific error (EINVAL) which tells the directory is not mounted.
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//
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// 4. After performing an unmount. If there is no error returned, the unmount succeeded.
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//
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// 5. To find the mount point root of a specific directory. You can perform os.Stat()
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// on the directory and traverse up until the Dev field of a parent directory differs.
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package mountinfo
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