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author | Nikolaus Rath <Nikolaus@rath.org> | 2017-08-04 22:12:36 +0200 |
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committer | Nikolaus Rath <Nikolaus@rath.org> | 2017-08-06 10:13:43 +0200 |
commit | ed0cfd8c7ce906b10aac895095545d199eafbcc6 (patch) | |
tree | 1a6eb32d9b9e47390cfa66b80b813e0713cde139 /include/fuse.h | |
parent | c36e7d528e87f2327bdb56ea2b1ada9e05cb08ac (diff) | |
download | libfuse-ed0cfd8c7ce906b10aac895095545d199eafbcc6.tar.gz |
Clarify how the filesystem should handle open/create flags
Diffstat (limited to 'include/fuse.h')
-rw-r--r-- | include/fuse.h | 59 |
1 files changed, 46 insertions, 13 deletions
diff --git a/include/fuse.h b/include/fuse.h index 19fd12c..25457f1 100644 --- a/include/fuse.h +++ b/include/fuse.h @@ -380,20 +380,53 @@ struct fuse_operations { */ int (*truncate) (const char *, off_t, struct fuse_file_info *fi); - /** File open operation + /** Open a file + * + * Open flags are available in fi->flags. The following rules + * apply. + * + * - Creation (O_CREAT, O_EXCL, O_NOCTTY) flags will be + * filtered out / handled by the kernel. + * + * - Access modes (O_RDONLY, O_WRONLY, O_RDWR) should be used + * by the filesystem to check if the operation is + * permitted. If the ``-o default_permissions`` mount + * option is given, this check is already done by the + * kernel before calling open() and may thus be omitted by + * the filesystem. + * + * - When writeback caching is enabled, the kernel may send + * read requests even for files opened with O_WRONLY. The + * filesystem should be prepared to handle this. + * + * - When writeback caching is disabled, the filesystem is + * expected to properly handle the O_APPEND flag and ensure + * that each write is appending to the end of the file. + * + * - When writeback caching is enabled, the kernel will + * handle O_APPEND. However, unless all changes to the file + * come through the kernel this will not work reliably. The + * filesystem should thus either ignore the O_APPEND flag + * (and let the kernel handle it), or return an error + * (indicating that reliably O_APPEND is not available). + * + * Filesystem may store an arbitrary file handle (pointer, + * index, etc) in fi->fh, and use this in other all other file + * operations (read, write, flush, release, fsync). + * + * Filesystem may also implement stateless file I/O and not store + * anything in fi->fh. + * + * There are also some flags (direct_io, keep_cache) which the + * filesystem may set in fi, to change the way the file is opened. + * See fuse_file_info structure in <fuse_common.h> for more details. + * + * If this request is answered with an error code of ENOSYS + * and FUSE_CAP_NO_OPEN_SUPPORT is set in + * `fuse_conn_info.capable`, this is treated as success and + * future calls to open will also succeed without being send + * to the filesystem process. * - * No creation (O_CREAT, O_EXCL) and by default also no - * truncation (O_TRUNC) flags will be passed to open(). If an - * application specifies O_TRUNC, fuse first calls truncate() - * and then open(). Only if 'atomic_o_trunc' has been - * specified and kernel version is 2.6.24 or later, O_TRUNC is - * passed on to open. - * - * Unless the 'default_permissions' mount option is given, - * open should check if the operation is permitted for the - * given flags. Optionally open may also return an arbitrary - * filehandle in the fuse_file_info structure, which will be - * passed to all file operations. */ int (*open) (const char *, struct fuse_file_info *); |