fs: sort out the fallocate mode vs flag mess

The fallocate system call takes a mode argument, but that argument
contains a wild mix of exclusive modes and an optional flags.

Replace FALLOC_FL_SUPPORTED_MASK with FALLOC_FL_MODE_MASK, which excludes
the optional flag bit, so that we can use switch statement on the value
to easily enumerate the cases while getting the check for duplicate modes
for free.

To make this (and in the future the file system implementations) more
readable also add a symbolic name for the 0 mode used to allocate blocks.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20240827065123.1762168-4-hch@lst.de
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/fs/open.c b/fs/open.c
index 22adbef7ecc2a6af5e28aa75de7df30385843408..daf1b55ca8180b161bfb1f14f0e4ce7140650555 100644 (file)
--- a/fs/open.c
+++ b/fs/open.c
@@ -252,40 +252,39 @@ int vfs_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
        if (offset < 0 || len <= 0)
                return -EINVAL;
 
-       /* Return error if mode is not supported */
-       if (mode & ~FALLOC_FL_SUPPORTED_MASK)
+       if (mode & ~(FALLOC_FL_MODE_MASK | FALLOC_FL_KEEP_SIZE))
                return -EOPNOTSUPP;
 
-       /* Punch hole and zero range are mutually exclusive */
-       if ((mode & (FALLOC_FL_PUNCH_HOLE | FALLOC_FL_ZERO_RANGE)) ==
-           (FALLOC_FL_PUNCH_HOLE | FALLOC_FL_ZERO_RANGE))
-               return -EOPNOTSUPP;
-
-       /* Punch hole must have keep size set */
-       if ((mode & FALLOC_FL_PUNCH_HOLE) &&
-           !(mode & FALLOC_FL_KEEP_SIZE))
+       /*
+        * Modes are exclusive, even if that is not obvious from the encoding
+        * as bit masks and the mix with the flag in the same namespace.
+        *
+        * To make things even more complicated, FALLOC_FL_ALLOCATE_RANGE is
+        * encoded as no bit set.
+        */
+       switch (mode & FALLOC_FL_MODE_MASK) {
+       case FALLOC_FL_ALLOCATE_RANGE:
+       case FALLOC_FL_UNSHARE_RANGE:
+       case FALLOC_FL_ZERO_RANGE:
+               break;
+       case FALLOC_FL_PUNCH_HOLE:
+               if (!(mode & FALLOC_FL_KEEP_SIZE))
+                       return -EOPNOTSUPP;
+               break;
+       case FALLOC_FL_COLLAPSE_RANGE:
+       case FALLOC_FL_INSERT_RANGE:
+               if (mode & FALLOC_FL_KEEP_SIZE)
+                       return -EOPNOTSUPP;
+               break;
+       default:
                return -EOPNOTSUPP;
-
-       /* Collapse range should only be used exclusively. */
-       if ((mode & FALLOC_FL_COLLAPSE_RANGE) &&
-           (mode & ~FALLOC_FL_COLLAPSE_RANGE))
-               return -EINVAL;
-
-       /* Insert range should only be used exclusively. */
-       if ((mode & FALLOC_FL_INSERT_RANGE) &&
-           (mode & ~FALLOC_FL_INSERT_RANGE))
-               return -EINVAL;
-
-       /* Unshare range should only be used with allocate mode. */
-       if ((mode & FALLOC_FL_UNSHARE_RANGE) &&
-           (mode & ~(FALLOC_FL_UNSHARE_RANGE | FALLOC_FL_KEEP_SIZE)))
-               return -EINVAL;
+       }
 
        if (!(file->f_mode & FMODE_WRITE))
                return -EBADF;
 
        /*
-        * We can only allow pure fallocate on append only files
+        * On append-only files only space preallocation is supported.
         */
        if ((mode & ~FALLOC_FL_KEEP_SIZE) && IS_APPEND(inode))
                return -EPERM;

diff --git a/include/linux/falloc.h b/include/linux/falloc.h
index f3f0b97b167579d130e8c1932572bcf22105a43f..3f49f3df6af5fb66fb09bb64657f867cd65ee691 100644 (file)
--- a/include/linux/falloc.h
+++ b/include/linux/falloc.h
@@ -25,12 +25,18 @@ struct space_resv {
 #define FS_IOC_UNRESVSP64      _IOW('X', 43, struct space_resv)
 #define FS_IOC_ZERO_RANGE      _IOW('X', 57, struct space_resv)
 
-#define        FALLOC_FL_SUPPORTED_MASK        (FALLOC_FL_KEEP_SIZE |          \
-                                        FALLOC_FL_PUNCH_HOLE |         \
-                                        FALLOC_FL_COLLAPSE_RANGE |     \
-                                        FALLOC_FL_ZERO_RANGE |         \
-                                        FALLOC_FL_INSERT_RANGE |       \
-                                        FALLOC_FL_UNSHARE_RANGE)
+/*
+ * Mask of all supported fallocate modes.  Only one can be set at a time.
+ *
+ * In addition to the mode bit, the mode argument can also encode flags.
+ * FALLOC_FL_KEEP_SIZE is the only supported flag so far.
+ */
+#define FALLOC_FL_MODE_MASK    (FALLOC_FL_ALLOCATE_RANGE |     \
+                                FALLOC_FL_PUNCH_HOLE |         \
+                                FALLOC_FL_COLLAPSE_RANGE |     \
+                                FALLOC_FL_ZERO_RANGE |         \
+                                FALLOC_FL_INSERT_RANGE |       \
+                                FALLOC_FL_UNSHARE_RANGE)
 
 /* on ia32 l_start is on a 32-bit boundary */
 #if defined(CONFIG_X86_64)

diff --git a/include/uapi/linux/falloc.h b/include/uapi/linux/falloc.h
index 51398fa57f6cdf65747410a79da53f759eade553..5810371ed72bbd85d2d63fe57767739cb854420e 100644 (file)
--- a/include/uapi/linux/falloc.h
+++ b/include/uapi/linux/falloc.h
@@ -2,6 +2,7 @@
 #ifndef _UAPI_FALLOC_H_
 #define _UAPI_FALLOC_H_
 
+#define FALLOC_FL_ALLOCATE_RANGE 0x00 /* allocate range */
 #define FALLOC_FL_KEEP_SIZE    0x01 /* default is extend size */
 #define FALLOC_FL_PUNCH_HOLE   0x02 /* de-allocates range */
 #define FALLOC_FL_NO_HIDE_STALE        0x04 /* reserved codepoint */