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![Taylor Blau](/assets/img/avatar_default.png)
In the next patch, 'hold_lock_file_for_update' will gain an additional 'mode' parameter to specify permissions for the associated temporary file. Since the lockfile.c machinery uses 'create_tempfile' which always creates a temporary file with global read-write permissions, introduce a variant here that allows specifying the mode. Note that the mode given to 'create_tempfile_mode' is not guaranteed to be written to disk, since it is subject to both the umask and 'core.sharedRepository'. Arguably, all temporary files should have permission 0444, since they are likely to be renamed into place and then not written to again. This is a much larger change than we may want to take on in this otherwise small patch, so for the time being, make 'create_tempfile' behave as it has always done by inlining it to 'create_tempfile_mode' with mode set to '0666'. Signed-off-by: Taylor Blau <me@ttaylorr.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
274 lines
9.4 KiB
C
274 lines
9.4 KiB
C
#ifndef TEMPFILE_H
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#define TEMPFILE_H
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#include "list.h"
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#include "strbuf.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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* * Attempts to create a temporary file by calling
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* `create_tempfile()`. The resources used for the temporary file are
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* managed by the tempfile API.
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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 `tempfile->fd` file descriptor
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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 created 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_gently()`, and later call
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* `delete_tempfile()` or `rename_tempfile()`.
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*
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* After the temporary file is renamed or deleted, the `tempfile`
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* object is no longer valid and should not be reused.
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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_gently()`. 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 an allocated tempfile on success or NULL
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* on failure. On errors, `errno` describes the reason for failure.
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*
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* `rename_tempfile()` and `close_tempfile_gently()` return 0 on success.
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* On failure they set `errno` appropriately and return -1.
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* `delete_tempfile()` and `rename` (but not `close`) do their best to
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* delete the temporary file before returning.
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*/
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struct tempfile {
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volatile struct volatile_list_head list;
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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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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 tempfile (whose "fd" member can be used for writing to it), or
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* NULL on error. It is an error if a file already exists at that path.
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* Note that `mode` will be further modified by the umask, and possibly
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* `core.sharedRepository`, so it is not guaranteed to have the given
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* mode.
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*/
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struct tempfile *create_tempfile_mode(const char *path, int mode);
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static inline struct tempfile *create_tempfile(const char *path)
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{
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return create_tempfile_mode(path, 0666);
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}
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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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struct tempfile *register_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 tempfile whose "fd" member is open
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* for writing the temporary file. On errors, they return NULL and set
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* errno appropriately (except for the "x" variants, which die() on
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* errors).
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*/
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/* See "mks_tempfile functions" above. */
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struct tempfile *mks_tempfile_sm(const char *filename_template,
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int suffixlen, int mode);
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/* See "mks_tempfile functions" above. */
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static inline struct tempfile *mks_tempfile_s(const char *filename_template,
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int suffixlen)
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{
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return mks_tempfile_sm(filename_template, suffixlen, 0600);
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}
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/* See "mks_tempfile functions" above. */
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static inline struct tempfile *mks_tempfile_m(const char *filename_template, int mode)
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{
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return mks_tempfile_sm(filename_template, 0, mode);
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}
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/* See "mks_tempfile functions" above. */
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static inline struct tempfile *mks_tempfile(const char *filename_template)
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{
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return mks_tempfile_sm(filename_template, 0, 0600);
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}
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/* See "mks_tempfile functions" above. */
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struct tempfile *mks_tempfile_tsm(const char *filename_template,
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int suffixlen, int mode);
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/* See "mks_tempfile functions" above. */
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static inline struct tempfile *mks_tempfile_ts(const char *filename_template,
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int suffixlen)
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{
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return mks_tempfile_tsm(filename_template, suffixlen, 0600);
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}
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/* See "mks_tempfile functions" above. */
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static inline struct tempfile *mks_tempfile_tm(const char *filename_template, int mode)
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{
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return mks_tempfile_tsm(filename_template, 0, mode);
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}
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/* See "mks_tempfile functions" above. */
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static inline struct tempfile *mks_tempfile_t(const char *filename_template)
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{
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return mks_tempfile_tsm(filename_template, 0, 0600);
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}
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/* See "mks_tempfile functions" above. */
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struct tempfile *xmks_tempfile_m(const char *filename_template, int mode);
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/* See "mks_tempfile functions" above. */
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static inline struct tempfile *xmks_tempfile(const char *filename_template)
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{
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return xmks_tempfile_m(filename_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_gently()` is called or
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* when the file is deleted or renamed.
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*/
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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 && 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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const char *get_tempfile_path(struct tempfile *tempfile);
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int get_tempfile_fd(struct tempfile *tempfile);
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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. Usually `delete_tempfile()` or `rename_tempfile()`
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* should eventually be called regardless of whether `close_tempfile_gently()`
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* succeeds.
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*/
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int close_tempfile_gently(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_gently()` 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_gently()` 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, truncating the existing
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* contents. Write out the new 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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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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void delete_tempfile(struct tempfile **tempfile_p);
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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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int rename_tempfile(struct tempfile **tempfile_p, const char *path);
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#endif /* TEMPFILE_H */
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