3 files changed, 69 insertions, 22 deletions

diff --git a/module/os/linux/zfs/zfs_vfsops.c b/module/os/linux/zfs/zfs_vfsops.c
index ea5971b0c..9561960bc 100644
--- a/module/os/linux/zfs/zfs_vfsops.c
+++ b/module/os/linux/zfs/zfs_vfsops.c
@@ -1088,9 +1088,9 @@ objs:
 }
 
 int
-zfs_statvfs(struct dentry *dentry, struct kstatfs *statp)
+zfs_statvfs(struct inode *ip, struct kstatfs *statp)
 {
-	zfsvfs_t *zfsvfs = dentry->d_sb->s_fs_info;
+	zfsvfs_t *zfsvfs = ITOZSB(ip);
 	uint64_t refdbytes, availbytes, usedobjs, availobjs;
 	int err = 0;
 
@@ -1148,7 +1148,7 @@ zfs_statvfs(struct dentry *dentry, struct kstatfs *statp)
 
 	if (dmu_objset_projectquota_enabled(zfsvfs->z_os) &&
 	    dmu_objset_projectquota_present(zfsvfs->z_os)) {
-		znode_t *zp = ITOZ(dentry->d_inode);
+		znode_t *zp = ITOZ(ip);
 
 		if (zp->z_pflags & ZFS_PROJINHERIT && zp->z_projid &&
 		    zpl_is_valid_projid(zp->z_projid))
diff --git a/module/os/linux/zfs/zpl_file.c b/module/os/linux/zfs/zpl_file.c
index 0fad63a4f..c26ed5d09 100644
--- a/module/os/linux/zfs/zpl_file.c
+++ b/module/os/linux/zfs/zpl_file.c
@@ -34,6 +34,11 @@
 #include <sys/zfs_vnops.h>
 #include <sys/zfs_project.h>
 
+/*
+ * When using fallocate(2) to preallocate space, inflate the requested
+ * capacity check by 10% to account for the required metadata blocks.
+ */
+unsigned int zfs_fallocate_reserve_percent = 110;
 
 static int
 zpl_open(struct inode *ip, struct file *filp)
@@ -721,20 +726,23 @@ zpl_writepage(struct page *pp, struct writeback_control *wbc)
 }
 
 /*
- * The only flag combination which matches the behavior of zfs_space()
- * is FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE.  The FALLOC_FL_PUNCH_HOLE
+ * The flag combination which matches the behavior of zfs_space() is
+ * FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE.  The FALLOC_FL_PUNCH_HOLE
  * flag was introduced in the 2.6.38 kernel.
+ *
+ * The original mode=0 (allocate space) behavior can be reasonably emulated
+ * by checking if enough space exists and creating a sparse file, as real
+ * persistent space reservation is not possible due to COW, snapshots, etc.
  */
 static long
 zpl_fallocate_common(struct inode *ip, int mode, loff_t offset, loff_t len)
 {
 	cred_t *cr = CRED();
-	flock64_t bf;
 	loff_t olen;
 	fstrans_cookie_t cookie;
-	int error;
+	int error = 0;
 
-	if (mode != (FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE))
+	if ((mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE)) != 0)
 		return (-EOPNOTSUPP);
 
 	if (offset < 0 || len <= 0)
@@ -743,21 +751,54 @@ zpl_fallocate_common(struct inode *ip, int mode, loff_t offset, loff_t len)
 	spl_inode_lock(ip);
 	olen = i_size_read(ip);
 
-	if (offset > olen) {
-		spl_inode_unlock(ip);
-		return (0);
-	}
-	if (offset + len > olen)
-		len = olen - offset;
-	bf.l_type = F_WRLCK;
-	bf.l_whence = SEEK_SET;
-	bf.l_start = offset;
-	bf.l_len = len;
-	bf.l_pid = 0;
-
 	crhold(cr);
 	cookie = spl_fstrans_mark();
-	error = -zfs_space(ITOZ(ip), F_FREESP, &bf, O_RDWR, offset, cr);
+	if (mode & FALLOC_FL_PUNCH_HOLE) {
+		flock64_t bf;
+
+		if (offset > olen)
+			goto out_unmark;
+
+		if (offset + len > olen)
+			len = olen - offset;
+		bf.l_type = F_WRLCK;
+		bf.l_whence = SEEK_SET;
+		bf.l_start = offset;
+		bf.l_len = len;
+		bf.l_pid = 0;
+
+		error = -zfs_space(ITOZ(ip), F_FREESP, &bf, O_RDWR, offset, cr);
+	} else if ((mode & ~FALLOC_FL_KEEP_SIZE) == 0) {
+		unsigned int percent = zfs_fallocate_reserve_percent;
+		struct kstatfs statfs;
+
+		/* Legacy mode, disable fallocate compatibility. */
+		if (percent == 0) {
+			error = -EOPNOTSUPP;
+			goto out_unmark;
+		}
+
+		/*
+		 * Use zfs_statvfs() instead of dmu_objset_space() since it
+		 * also checks project quota limits, which are relevant here.
+		 */
+		error = zfs_statvfs(ip, &statfs);
+		if (error)
+			goto out_unmark;
+
+		/*
+		 * Shrink available space a bit to account for overhead/races.
+		 * We know the product previously fit into availbytes from
+		 * dmu_objset_space(), so the smaller product will also fit.
+		 */
+		if (len > statfs.f_bavail * (statfs.f_bsize * 100 / percent)) {
+			error = -ENOSPC;
+			goto out_unmark;
+		}
+		if (!(mode & FALLOC_FL_KEEP_SIZE) && offset + len > olen)
+			error = zfs_freesp(ITOZ(ip), offset + len, 0, 0, FALSE);
+	}
+out_unmark:
 	spl_fstrans_unmark(cookie);
 	spl_inode_unlock(ip);
 
@@ -1030,3 +1071,9 @@ const struct file_operations zpl_dir_file_operations = {
 	.compat_ioctl   = zpl_compat_ioctl,
 #endif
 };
+
+/* BEGIN CSTYLED */
+module_param(zfs_fallocate_reserve_percent, uint, 0644);
+MODULE_PARM_DESC(zfs_fallocate_reserve_percent,
+    "Percentage of length to use for the available capacity check");
+/* END CSTYLED */
diff --git a/module/os/linux/zfs/zpl_super.c b/module/os/linux/zfs/zpl_super.c
index 08cf75862..75adff517 100644
--- a/module/os/linux/zfs/zpl_super.c
+++ b/module/os/linux/zfs/zpl_super.c
@@ -138,7 +138,7 @@ zpl_statfs(struct dentry *dentry, struct kstatfs *statp)
 	int error;
 
 	cookie = spl_fstrans_mark();
-	error = -zfs_statvfs(dentry, statp);
+	error = -zfs_statvfs(dentry->d_inode, statp);
 	spl_fstrans_unmark(cookie);
 	ASSERT3S(error, <=, 0);