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![Ben Wijen](/assets/img/avatar_default.png)
When the index is locked and child processes inherit the handle to said lock and the parent process wants to remove the lock before the child process exits, on Windows there is a problem: it won't work because files cannot be deleted if a process holds a handle on them. The symptom: Rename from 'xxx/.git/index.lock' to 'xxx/.git/index' failed. Should I try again? (y/n) Spawning child processes with bInheritHandles==FALSE would not work because no file handles would be inherited, not even the hStdXxx handles in STARTUPINFO (stdin/stdout/stderr). Opening every file with O_NOINHERIT does not work, either, as e.g. git-upload-pack expects inherited file handles. This leaves us with the only way out: creating temp files with the O_NOINHERIT flag. This flag is Windows-specific, however. For our purposes, it is equivalent to O_CLOEXEC (which does not exist on Windows), so let's just open temporary files with the O_CLOEXEC flag and map that flag to O_NOINHERIT on Windows. As Eric Wong pointed out, we need to be careful to handle the case where the Linux headers used to compile Git support O_CLOEXEC but the Linux kernel used to run Git does not: it returns an EINVAL. This fixes the test that we just introduced to demonstrate the problem. Signed-off-by: Ben Wijen <ben@wijen.net> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>
276 lines
9.5 KiB
C
276 lines
9.5 KiB
C
#ifndef TEMPFILE_H
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#define TEMPFILE_H
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/*
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* Handle temporary files.
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*
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* The tempfile API allows temporary files to be created, deleted, and
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* atomically renamed. Temporary files that are still active when the
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* program ends are cleaned up automatically. Lockfiles (see
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* "lockfile.h") are built on top of this API.
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*
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*
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* Calling sequence
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* ----------------
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*
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* The caller:
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*
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* * Allocates a `struct tempfile` either as a static variable or on
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* the heap, initialized to zeros. Once you use the structure to
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* call `create_tempfile()`, it belongs to the tempfile subsystem
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* and its storage must remain valid throughout the life of the
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* program (i.e. you cannot use an on-stack variable to hold this
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* structure).
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*
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* * Attempts to create a temporary file by calling
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* `create_tempfile()`.
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*
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* * Writes new content to the file by either:
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*
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* * writing to the file descriptor returned by `create_tempfile()`
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* (also available via `tempfile->fd`).
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*
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* * calling `fdopen_tempfile()` to get a `FILE` pointer for the
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* open file and writing to the file using stdio.
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*
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* Note that the file descriptor returned by create_tempfile()
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* is marked O_CLOEXEC, so the new contents must be written by
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* the current process, not any spawned one.
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*
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* When finished writing, the caller can:
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*
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* * Close the file descriptor and remove the temporary file by
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* calling `delete_tempfile()`.
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*
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* * Close the temporary file and rename it atomically to a specified
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* filename by calling `rename_tempfile()`. This relinquishes
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* control of the file.
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*
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* * Close the file descriptor without removing or renaming the
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* temporary file by calling `close_tempfile()`, and later call
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* `delete_tempfile()` or `rename_tempfile()`.
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*
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* Even after the temporary file is renamed or deleted, the `tempfile`
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* object must not be freed or altered by the caller. However, it may
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* be reused; just pass it to another call of `create_tempfile()`.
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*
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* If the program exits before `rename_tempfile()` or
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* `delete_tempfile()` is called, an `atexit(3)` handler will close
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* and remove the temporary file.
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*
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* If you need to close the file descriptor yourself, do so by calling
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* `close_tempfile()`. You should never call `close(2)` or `fclose(3)`
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* yourself, otherwise the `struct tempfile` structure would still
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* think that the file descriptor needs to be closed, and a later
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* cleanup would result in duplicate calls to `close(2)`. Worse yet,
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* if you close and then later open another file descriptor for a
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* completely different purpose, then the unrelated file descriptor
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* might get closed.
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*
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*
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* Error handling
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* --------------
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*
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* `create_tempfile()` returns a file descriptor on success or -1 on
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* failure. On errors, `errno` describes the reason for failure.
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*
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* `delete_tempfile()`, `rename_tempfile()`, and `close_tempfile()`
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* return 0 on success. On failure they set `errno` appropriately, do
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* their best to delete the temporary file, and return -1.
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*/
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struct tempfile {
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struct tempfile *volatile next;
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volatile sig_atomic_t active;
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volatile int fd;
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FILE *volatile fp;
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volatile pid_t owner;
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char on_list;
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struct strbuf filename;
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};
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/*
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* Attempt to create a temporary file at the specified `path`. Return
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* a file descriptor for writing to it, or -1 on error. It is an error
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* if a file already exists at that path.
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*/
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extern int create_tempfile(struct tempfile *tempfile, const char *path);
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/*
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* Register an existing file as a tempfile, meaning that it will be
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* deleted when the program exits. The tempfile is considered closed,
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* but it can be worked with like any other closed tempfile (for
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* example, it can be opened using reopen_tempfile()).
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*/
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extern void register_tempfile(struct tempfile *tempfile, const char *path);
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/*
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* mks_tempfile functions
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*
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* The following functions attempt to create and open temporary files
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* with names derived automatically from a template, in the manner of
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* mkstemps(), and arrange for them to be deleted if the program ends
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* before they are deleted explicitly. There is a whole family of such
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* functions, named according to the following pattern:
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*
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* x?mks_tempfile_t?s?m?()
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*
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* The optional letters have the following meanings:
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*
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* x - die if the temporary file cannot be created.
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*
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* t - create the temporary file under $TMPDIR (as opposed to
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* relative to the current directory). When these variants are
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* used, template should be the pattern for the filename alone,
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* without a path.
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*
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* s - template includes a suffix that is suffixlen characters long.
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*
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* m - the temporary file should be created with the specified mode
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* (otherwise, the mode is set to 0600).
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*
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* None of these functions modify template. If the caller wants to
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* know the (absolute) path of the file that was created, it can be
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* read from tempfile->filename.
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*
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* On success, the functions return a file descriptor that is open for
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* writing the temporary file. On errors, they return -1 and set errno
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* appropriately (except for the "x" variants, which die() on errors).
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*/
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/* See "mks_tempfile functions" above. */
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extern int mks_tempfile_sm(struct tempfile *tempfile,
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const char *template, int suffixlen, int mode);
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/* See "mks_tempfile functions" above. */
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static inline int mks_tempfile_s(struct tempfile *tempfile,
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const char *template, int suffixlen)
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{
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return mks_tempfile_sm(tempfile, template, suffixlen, 0600);
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}
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/* See "mks_tempfile functions" above. */
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static inline int mks_tempfile_m(struct tempfile *tempfile,
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const char *template, int mode)
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{
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return mks_tempfile_sm(tempfile, template, 0, mode);
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}
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/* See "mks_tempfile functions" above. */
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static inline int mks_tempfile(struct tempfile *tempfile,
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const char *template)
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{
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return mks_tempfile_sm(tempfile, template, 0, 0600);
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}
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/* See "mks_tempfile functions" above. */
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extern int mks_tempfile_tsm(struct tempfile *tempfile,
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const char *template, int suffixlen, int mode);
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/* See "mks_tempfile functions" above. */
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static inline int mks_tempfile_ts(struct tempfile *tempfile,
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const char *template, int suffixlen)
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{
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return mks_tempfile_tsm(tempfile, template, suffixlen, 0600);
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}
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/* See "mks_tempfile functions" above. */
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static inline int mks_tempfile_tm(struct tempfile *tempfile,
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const char *template, int mode)
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{
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return mks_tempfile_tsm(tempfile, template, 0, mode);
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}
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/* See "mks_tempfile functions" above. */
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static inline int mks_tempfile_t(struct tempfile *tempfile,
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const char *template)
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{
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return mks_tempfile_tsm(tempfile, template, 0, 0600);
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}
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/* See "mks_tempfile functions" above. */
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extern int xmks_tempfile_m(struct tempfile *tempfile,
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const char *template, int mode);
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/* See "mks_tempfile functions" above. */
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static inline int xmks_tempfile(struct tempfile *tempfile,
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const char *template)
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{
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return xmks_tempfile_m(tempfile, template, 0600);
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}
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/*
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* Associate a stdio stream with the temporary file (which must still
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* be open). Return `NULL` (*without* deleting the file) on error. The
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* stream is closed automatically when `close_tempfile()` is called or
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* when the file is deleted or renamed.
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*/
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extern FILE *fdopen_tempfile(struct tempfile *tempfile, const char *mode);
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static inline int is_tempfile_active(struct tempfile *tempfile)
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{
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return tempfile->active;
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}
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/*
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* Return the path of the lockfile. The return value is a pointer to a
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* field within the lock_file object and should not be freed.
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*/
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extern const char *get_tempfile_path(struct tempfile *tempfile);
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extern int get_tempfile_fd(struct tempfile *tempfile);
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extern FILE *get_tempfile_fp(struct tempfile *tempfile);
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/*
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* If the temporary file is still open, close it (and the file pointer
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* too, if it has been opened using `fdopen_tempfile()`) without
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* deleting the file. Return 0 upon success. On failure to `close(2)`,
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* return a negative value and delete the file. Usually
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* `delete_tempfile()` or `rename_tempfile()` should eventually be
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* called if `close_tempfile()` succeeds.
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*/
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extern int close_tempfile(struct tempfile *tempfile);
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/*
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* Re-open a temporary file that has been closed using
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* `close_tempfile()` but not yet deleted or renamed. This can be used
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* to implement a sequence of operations like the following:
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*
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* * Create temporary file.
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*
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* * Write new contents to file, then `close_tempfile()` to cause the
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* contents to be written to disk.
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*
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* * Pass the name of the temporary file to another program to allow
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* it (and nobody else) to inspect or even modify the file's
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* contents.
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*
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* * `reopen_tempfile()` to reopen the temporary file. Make further
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* updates to the contents.
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*
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* * `rename_tempfile()` to move the file to its permanent location.
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*/
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extern int reopen_tempfile(struct tempfile *tempfile);
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/*
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* Close the file descriptor and/or file pointer and remove the
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* temporary file associated with `tempfile`. It is a NOOP to call
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* `delete_tempfile()` for a `tempfile` object that has already been
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* deleted or renamed.
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*/
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extern void delete_tempfile(struct tempfile *tempfile);
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/*
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* Close the file descriptor and/or file pointer if they are still
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* open, and atomically rename the temporary file to `path`. `path`
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* must be on the same filesystem as the lock file. Return 0 on
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* success. On failure, delete the temporary file and return -1, with
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* `errno` set to the value from the failing call to `close(2)` or
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* `rename(2)`. It is a bug to call `rename_tempfile()` for a
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* `tempfile` object that is not currently active.
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*/
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extern int rename_tempfile(struct tempfile *tempfile, const char *path);
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#endif /* TEMPFILE_H */
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