linux-kernel - [PATCH 17/21] filemap: add FGP_CREAT

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Message-Id: <20240227232100.478238-18-pbonzini@redhat.com>
Date: Tue, 27 Feb 2024 18:20:56 -0500
From: Paolo Bonzini <pbonzini@...hat.com>
To: linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org
Cc: seanjc@...gle.com,
	michael.roth@....com,
	isaku.yamahata@...el.com,
	thomas.lendacky@....com
Subject: [PATCH 17/21] filemap: add FGP_CREAT_ONLY

Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
 include/linux/pagemap.h | 2 ++
 mm/filemap.c            | 4 ++++
 2 files changed, 6 insertions(+)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 2df35e65557d..e8ac0b32f84d 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -586,6 +586,7 @@ pgoff_t page_cache_prev_miss(struct address_space *mapping,
  * * %FGP_CREAT - If no folio is present then a new folio is allocated,
  *   added to the page cache and the VM's LRU list.  The folio is
  *   returned locked.
+ * * %FGP_CREAT_ONLY - Fail if a folio is not present
  * * %FGP_FOR_MMAP - The caller wants to do its own locking dance if the
  *   folio is already in cache.  If the folio was allocated, unlock it
  *   before returning so the caller can do the same dance.
@@ -606,6 +607,7 @@ typedef unsigned int __bitwise fgf_t;
 #define FGP_NOWAIT		((__force fgf_t)0x00000020)
 #define FGP_FOR_MMAP		((__force fgf_t)0x00000040)
 #define FGP_STABLE		((__force fgf_t)0x00000080)
+#define FGP_CREAT_ONLY		((__force fgf_t)0x00000100)
 #define FGF_GET_ORDER(fgf)	(((__force unsigned)fgf) >> 26)	/* top 6 bits */
 
 #define FGP_WRITEBEGIN		(FGP_LOCK | FGP_WRITE | FGP_CREAT | FGP_STABLE)
diff --git a/mm/filemap.c b/mm/filemap.c
index 750e779c23db..d5107bd0cd09 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1854,6 +1854,10 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
 		folio = NULL;
 	if (!folio)
 		goto no_page;
+	if (fgp_flags & FGP_CREAT_ONLY) {
+		folio_put(folio);
+		return ERR_PTR(-EEXIST);
+	}
 
 	if (fgp_flags & FGP_LOCK) {
 		if (fgp_flags & FGP_NOWAIT) {
-- 
2.39.0