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Diffstat (limited to 'tempfile.h')
| -rw-r--r-- | tempfile.h | 273 |
1 files changed, 273 insertions, 0 deletions
diff --git a/tempfile.h b/tempfile.h new file mode 100644 index 0000000000..4de3bc77d2 --- /dev/null +++ b/tempfile.h @@ -0,0 +1,273 @@ +#ifndef TEMPFILE_H +#define TEMPFILE_H + +#include "list.h" +#include "strbuf.h" + +/* + * Handle temporary files. + * + * The tempfile API allows temporary files to be created, deleted, and + * atomically renamed. Temporary files that are still active when the + * program ends are cleaned up automatically. Lockfiles (see + * "lockfile.h") are built on top of this API. + * + * + * Calling sequence + * ---------------- + * + * The caller: + * + * * Attempts to create a temporary file by calling + * `create_tempfile()`. The resources used for the temporary file are + * managed by the tempfile API. + * + * * Writes new content to the file by either: + * + * * writing to the `tempfile->fd` file descriptor + * + * * calling `fdopen_tempfile()` to get a `FILE` pointer for the + * open file and writing to the file using stdio. + * + * Note that the file descriptor created by create_tempfile() + * is marked O_CLOEXEC, so the new contents must be written by + * the current process, not any spawned one. + * + * When finished writing, the caller can: + * + * * Close the file descriptor and remove the temporary file by + * calling `delete_tempfile()`. + * + * * Close the temporary file and rename it atomically to a specified + * filename by calling `rename_tempfile()`. This relinquishes + * control of the file. + * + * * Close the file descriptor without removing or renaming the + * temporary file by calling `close_tempfile_gently()`, and later call + * `delete_tempfile()` or `rename_tempfile()`. + * + * After the temporary file is renamed or deleted, the `tempfile` + * object is no longer valid and should not be reused. + * + * If the program exits before `rename_tempfile()` or + * `delete_tempfile()` is called, an `atexit(3)` handler will close + * and remove the temporary file. + * + * If you need to close the file descriptor yourself, do so by calling + * `close_tempfile_gently()`. You should never call `close(2)` or `fclose(3)` + * yourself, otherwise the `struct tempfile` structure would still + * think that the file descriptor needs to be closed, and a later + * cleanup would result in duplicate calls to `close(2)`. Worse yet, + * if you close and then later open another file descriptor for a + * completely different purpose, then the unrelated file descriptor + * might get closed. + * + * + * Error handling + * -------------- + * + * `create_tempfile()` returns an allocated tempfile on success or NULL + * on failure. On errors, `errno` describes the reason for failure. + * + * `rename_tempfile()` and `close_tempfile_gently()` return 0 on success. + * On failure they set `errno` appropriately and return -1. + * `delete_tempfile()` and `rename` (but not `close`) do their best to + * delete the temporary file before returning. + */ + +struct tempfile { + volatile struct volatile_list_head list; + volatile sig_atomic_t active; + volatile int fd; + FILE *volatile fp; + volatile pid_t owner; + struct strbuf filename; +}; + +/* + * Attempt to create a temporary file at the specified `path`. Return + * a tempfile (whose "fd" member can be used for writing to it), or + * NULL on error. It is an error if a file already exists at that path. + * Note that `mode` will be further modified by the umask, and possibly + * `core.sharedRepository`, so it is not guaranteed to have the given + * mode. + */ +struct tempfile *create_tempfile_mode(const char *path, int mode); + +static inline struct tempfile *create_tempfile(const char *path) +{ + return create_tempfile_mode(path, 0666); +} + +/* + * Register an existing file as a tempfile, meaning that it will be + * deleted when the program exits. The tempfile is considered closed, + * but it can be worked with like any other closed tempfile (for + * example, it can be opened using reopen_tempfile()). + */ +struct tempfile *register_tempfile(const char *path); + + +/* + * mks_tempfile functions + * + * The following functions attempt to create and open temporary files + * with names derived automatically from a template, in the manner of + * mkstemps(), and arrange for them to be deleted if the program ends + * before they are deleted explicitly. There is a whole family of such + * functions, named according to the following pattern: + * + * x?mks_tempfile_t?s?m?() + * + * The optional letters have the following meanings: + * + * x - die if the temporary file cannot be created. + * + * t - create the temporary file under $TMPDIR (as opposed to + * relative to the current directory). When these variants are + * used, template should be the pattern for the filename alone, + * without a path. + * + * s - template includes a suffix that is suffixlen characters long. + * + * m - the temporary file should be created with the specified mode + * (otherwise, the mode is set to 0600). + * + * None of these functions modify template. If the caller wants to + * know the (absolute) path of the file that was created, it can be + * read from tempfile->filename. + * + * On success, the functions return a tempfile whose "fd" member is open + * for writing the temporary file. On errors, they return NULL and set + * errno appropriately (except for the "x" variants, which die() on + * errors). + */ + +/* See "mks_tempfile functions" above. */ +struct tempfile *mks_tempfile_sm(const char *filename_template, + int suffixlen, int mode); + +/* See "mks_tempfile functions" above. */ +static inline struct tempfile *mks_tempfile_s(const char *filename_template, + int suffixlen) +{ + return mks_tempfile_sm(filename_template, suffixlen, 0600); +} + +/* See "mks_tempfile functions" above. */ +static inline struct tempfile *mks_tempfile_m(const char *filename_template, int mode) +{ + return mks_tempfile_sm(filename_template, 0, mode); +} + +/* See "mks_tempfile functions" above. */ +static inline struct tempfile *mks_tempfile(const char *filename_template) +{ + return mks_tempfile_sm(filename_template, 0, 0600); +} + +/* See "mks_tempfile functions" above. */ +struct tempfile *mks_tempfile_tsm(const char *filename_template, + int suffixlen, int mode); + +/* See "mks_tempfile functions" above. */ +static inline struct tempfile *mks_tempfile_ts(const char *filename_template, + int suffixlen) +{ + return mks_tempfile_tsm(filename_template, suffixlen, 0600); +} + +/* See "mks_tempfile functions" above. */ +static inline struct tempfile *mks_tempfile_tm(const char *filename_template, int mode) +{ + return mks_tempfile_tsm(filename_template, 0, mode); +} + +/* See "mks_tempfile functions" above. */ +static inline struct tempfile *mks_tempfile_t(const char *filename_template) +{ + return mks_tempfile_tsm(filename_template, 0, 0600); +} + +/* See "mks_tempfile functions" above. */ +struct tempfile *xmks_tempfile_m(const char *filename_template, int mode); + +/* See "mks_tempfile functions" above. */ +static inline struct tempfile *xmks_tempfile(const char *filename_template) +{ + return xmks_tempfile_m(filename_template, 0600); +} + +/* + * Associate a stdio stream with the temporary file (which must still + * be open). Return `NULL` (*without* deleting the file) on error. The + * stream is closed automatically when `close_tempfile_gently()` is called or + * when the file is deleted or renamed. + */ +FILE *fdopen_tempfile(struct tempfile *tempfile, const char *mode); + +static inline int is_tempfile_active(struct tempfile *tempfile) +{ + return tempfile && tempfile->active; +} + +/* + * Return the path of the lockfile. The return value is a pointer to a + * field within the lock_file object and should not be freed. + */ +const char *get_tempfile_path(struct tempfile *tempfile); + +int get_tempfile_fd(struct tempfile *tempfile); +FILE *get_tempfile_fp(struct tempfile *tempfile); + +/* + * If the temporary file is still open, close it (and the file pointer + * too, if it has been opened using `fdopen_tempfile()`) without + * deleting the file. Return 0 upon success. On failure to `close(2)`, + * return a negative value. Usually `delete_tempfile()` or `rename_tempfile()` + * should eventually be called regardless of whether `close_tempfile_gently()` + * succeeds. + */ +int close_tempfile_gently(struct tempfile *tempfile); + +/* + * Re-open a temporary file that has been closed using + * `close_tempfile_gently()` but not yet deleted or renamed. This can be used + * to implement a sequence of operations like the following: + * + * * Create temporary file. + * + * * Write new contents to file, then `close_tempfile_gently()` to cause the + * contents to be written to disk. + * + * * Pass the name of the temporary file to another program to allow + * it (and nobody else) to inspect or even modify the file's + * contents. + * + * * `reopen_tempfile()` to reopen the temporary file, truncating the existing + * contents. Write out the new contents. + * + * * `rename_tempfile()` to move the file to its permanent location. + */ +int reopen_tempfile(struct tempfile *tempfile); + +/* + * Close the file descriptor and/or file pointer and remove the + * temporary file associated with `tempfile`. It is a NOOP to call + * `delete_tempfile()` for a `tempfile` object that has already been + * deleted or renamed. + */ +void delete_tempfile(struct tempfile **tempfile_p); + +/* + * Close the file descriptor and/or file pointer if they are still + * open, and atomically rename the temporary file to `path`. `path` + * must be on the same filesystem as the lock file. Return 0 on + * success. On failure, delete the temporary file and return -1, with + * `errno` set to the value from the failing call to `close(2)` or + * `rename(2)`. It is a bug to call `rename_tempfile()` for a + * `tempfile` object that is not currently active. + */ +int rename_tempfile(struct tempfile **tempfile_p, const char *path); + +#endif /* TEMPFILE_H */ |