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[88.21.68.214]) by smtp.gmail.com with ESMTPSA id o16sm18658397ejj.106.2020.08.04.05.25.21 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 04 Aug 2020 05:25:22 -0700 (PDT) Subject: Re: [PATCH 1/3] memory: add readonly support to memory_region_init_ram_from_file() To: Stefan Hajnoczi , qemu-devel@nongnu.org References: <20200804101244.1283503-1-stefanha@redhat.com> <20200804101244.1283503-2-stefanha@redhat.com> From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= Autocrypt: addr=philmd@redhat.com; keydata= mQINBDXML8YBEADXCtUkDBKQvNsQA7sDpw6YLE/1tKHwm24A1au9Hfy/OFmkpzo+MD+dYc+7 bvnqWAeGweq2SDq8zbzFZ1gJBd6+e5v1a/UrTxvwBk51yEkadrpRbi+r2bDpTJwXc/uEtYAB GvsTZMtiQVA4kRID1KCdgLa3zztPLCj5H1VZhqZsiGvXa/nMIlhvacRXdbgllPPJ72cLUkXf z1Zu4AkEKpccZaJspmLWGSzGu6UTZ7UfVeR2Hcc2KI9oZB1qthmZ1+PZyGZ/Dy+z+zklC0xl XIpQPmnfy9+/1hj1LzJ+pe3HzEodtlVA+rdttSvA6nmHKIt8Ul6b/h1DFTmUT1lN1WbAGxmg CH1O26cz5nTrzdjoqC/b8PpZiT0kO5MKKgiu5S4PRIxW2+RA4H9nq7nztNZ1Y39bDpzwE5Sp bDHzd5owmLxMLZAINtCtQuRbSOcMjZlg4zohA9TQP9krGIk+qTR+H4CV22sWldSkVtsoTaA2 qNeSJhfHQY0TyQvFbqRsSNIe2gTDzzEQ8itsmdHHE/yzhcCVvlUzXhAT6pIN0OT+cdsTTfif MIcDboys92auTuJ7U+4jWF1+WUaJ8gDL69ThAsu7mGDBbm80P3vvUZ4fQM14NkxOnuGRrJxO qjWNJ2ZUxgyHAh5TCxMLKWZoL5hpnvx3dF3Ti9HW2dsUUWICSQARAQABtDJQaGlsaXBwZSBN YXRoaWV1LURhdWTDqSAoUGhpbCkgPHBoaWxtZEByZWRoYXQuY29tPokCVQQTAQgAPwIbDwYL CQgHAwIGFQgCCQoLBBYCAwECHgECF4AWIQSJweePYB7obIZ0lcuio/1u3q3A3gUCXsfWwAUJ KtymWgAKCRCio/1u3q3A3ircD/9Vjh3aFNJ3uF3hddeoFg1H038wZr/xi8/rX27M1Vj2j9VH 0B8Olp4KUQw/hyO6kUxqkoojmzRpmzvlpZ0cUiZJo2bQIWnvScyHxFCv33kHe+YEIqoJlaQc JfKYlbCoubz+02E2A6bFD9+BvCY0LBbEj5POwyKGiDMjHKCGuzSuDRbCn0Mz4kCa7nFMF5Jv piC+JemRdiBd6102ThqgIsyGEBXuf1sy0QIVyXgaqr9O2b/0VoXpQId7yY7OJuYYxs7kQoXI 6WzSMpmuXGkmfxOgbc/L6YbzB0JOriX0iRClxu4dEUg8Bs2pNnr6huY2Ft+qb41RzCJvvMyu gS32LfN0bTZ6Qm2A8ayMtUQgnwZDSO23OKgQWZVglGliY3ezHZ6lVwC24Vjkmq/2yBSLakZE 6DZUjZzCW1nvtRK05ebyK6tofRsx8xB8pL/kcBb9nCuh70aLR+5cmE41X4O+MVJbwfP5s/RW 9BFSL3qgXuXso/3XuWTQjJJGgKhB6xXjMmb1J4q/h5IuVV4juv1Fem9sfmyrh+Wi5V1IzKI7 RPJ3KVb937eBgSENk53P0gUorwzUcO+ASEo3Z1cBKkJSPigDbeEjVfXQMzNt0oDRzpQqH2vp apo2jHnidWt8BsckuWZpxcZ9+/9obQ55DyVQHGiTN39hkETy3Emdnz1JVHTU0Q== Message-ID: Date: Tue, 4 Aug 2020 14:25:20 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <20200804101244.1283503-2-stefanha@redhat.com> Content-Language: en-US X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=205.139.110.61; envelope-from=philmd@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/08/04 01:28:16 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -40 X-Spam_score: -4.1 X-Spam_bar: ---- X-Spam_report: (-4.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Xiao Guangrong , "Michael S. Tsirkin" , Julio Montes , Igor Mammedov , Paolo Bonzini , Richard Henderson , Eduardo Habkost Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Hi Stefan, On 8/4/20 12:12 PM, Stefan Hajnoczi wrote: > There is currently no way to open(O_RDONLY) and mmap(PROT_READ) when > creating a memory region from a file. This functionality is needed since > the underlying host file may not allow writing. > > Add a bool readonly argument to memory_region_init_ram_from_file() and > the APIs it calls. > > Extend memory_region_init_ram_from_file() rather than introducing a > memory_region_init_rom_from_file() API so that callers can easily make a > choice between read/write and read-only at runtime without calling > different APIs. What happens if we call: memory_region_init_ram_from_file(mr, ..., readonly=false, ...); memory_region_set_readonly(mr, false); ? > > No new RAMBlock flag is introduced for read-only because it's unclear > whether RAMBlocks need to know that they are read-only. Pass a bool > readonly argument instead. > > Both of these design decisions can be changed in the future. It just > seemed like the simplest approach to me. > > Signed-off-by: Stefan Hajnoczi > --- > include/exec/memory.h | 2 ++ > include/exec/ram_addr.h | 5 +++-- > include/qemu/mmap-alloc.h | 2 ++ > backends/hostmem-file.c | 2 +- > exec.c | 18 +++++++++++------- > softmmu/memory.c | 7 +++++-- > util/mmap-alloc.c | 10 ++++++---- > util/oslib-posix.c | 2 +- > 8 files changed, 31 insertions(+), 17 deletions(-) > > diff --git a/include/exec/memory.h b/include/exec/memory.h > index 307e527835..1ae7b31e3a 100644 > --- a/include/exec/memory.h > +++ b/include/exec/memory.h > @@ -884,6 +884,7 @@ void memory_region_init_resizeable_ram(MemoryRegion *mr, > * - RAM_PMEM: the memory is persistent memory > * Other bits are ignored now. > * @path: the path in which to allocate the RAM. > + * @readonly: true to open @path for reading, false for read/write. > * @errp: pointer to Error*, to store an error if it happens. > * > * Note that this function does not do anything to cause the data in the > @@ -896,6 +897,7 @@ void memory_region_init_ram_from_file(MemoryRegion *mr, > uint64_t align, > uint32_t ram_flags, > const char *path, > + bool readonly, > Error **errp); > [...] > diff --git a/softmmu/memory.c b/softmmu/memory.c > index af25987518..d228635bb3 100644 > --- a/softmmu/memory.c > +++ b/softmmu/memory.c > @@ -1553,15 +1553,18 @@ void memory_region_init_ram_from_file(MemoryRegion *mr, > uint64_t align, > uint32_t ram_flags, > const char *path, > + bool readonly, > Error **errp) > { > Error *err = NULL; > memory_region_init(mr, owner, name, size); > mr->ram = true; > + mr->readonly = readonly; > mr->terminates = true; > mr->destructor = memory_region_destructor_ram; > mr->align = align; > - mr->ram_block = qemu_ram_alloc_from_file(size, mr, ram_flags, path, &err); > + mr->ram_block = qemu_ram_alloc_from_file(size, mr, ram_flags, path, > + readonly, &err); > mr->dirty_log_mask = tcg_enabled() ? (1 << DIRTY_MEMORY_CODE) : 0; > if (err) { > mr->size = int128_zero(); > @@ -1585,7 +1588,7 @@ void memory_region_init_ram_from_fd(MemoryRegion *mr, > mr->destructor = memory_region_destructor_ram; > mr->ram_block = qemu_ram_alloc_from_fd(size, mr, > share ? RAM_SHARED : 0, > - fd, &err); > + fd, false, &err); > mr->dirty_log_mask = tcg_enabled() ? (1 << DIRTY_MEMORY_CODE) : 0; > if (err) { > mr->size = int128_zero(); > diff --git a/util/mmap-alloc.c b/util/mmap-alloc.c > index 27dcccd8ec..890fda6a35 100644 > --- a/util/mmap-alloc.c > +++ b/util/mmap-alloc.c > @@ -85,9 +85,11 @@ size_t qemu_mempath_getpagesize(const char *mem_path) > void *qemu_ram_mmap(int fd, > size_t size, > size_t align, > + bool readonly, > bool shared, > bool is_pmem) > { > + int prot; > int flags; > int map_sync_flags = 0; > int guardfd; > @@ -146,8 +148,9 @@ void *qemu_ram_mmap(int fd, > > offset = QEMU_ALIGN_UP((uintptr_t)guardptr, align) - (uintptr_t)guardptr; > > - ptr = mmap(guardptr + offset, size, PROT_READ | PROT_WRITE, > - flags | map_sync_flags, fd, 0); > + prot = PROT_READ | (readonly ? 0 : PROT_WRITE); > + > + ptr = mmap(guardptr + offset, size, prot, flags | map_sync_flags, fd, 0); > > if (ptr == MAP_FAILED && map_sync_flags) { > if (errno == ENOTSUP) { > @@ -171,8 +174,7 @@ void *qemu_ram_mmap(int fd, > * if map failed with MAP_SHARED_VALIDATE | MAP_SYNC, > * we will remove these flags to handle compatibility. > */ > - ptr = mmap(guardptr + offset, size, PROT_READ | PROT_WRITE, > - flags, fd, 0); > + ptr = mmap(guardptr + offset, size, prot, flags, fd, 0); > } > > if (ptr == MAP_FAILED) { [...]